Heat-tolerant versus heat-sensitive Bos taurus cattle: influence of air temperature and breed on the metabolic response to a provocative immune challenge

The response of the immune and stress systems have been assessed in response to a lipopolysaccharide (LPS) challenge, yet the role of metabolism in mediating energy requirements during the acute phase response has not been sufficiently studied. This study tested heat-tolerant (Romosinuano [RO]) and heat-sensitive (Angus [ANG]) Bos taurus breeds at different ambient temperatures (T_a) to determine differential metabolic responses to LPS challenge. Twenty-one heifers (ANG: n = 11, 306 ± 26 kg BW; RO: n = 10, 313 ± 32 kg BW) were housed in stanchions in 4 temperature-controlled chambers. Initially, T_a in all 4 chambers was cycling at thermoneutrality (TN; 18.5°C–23.5°C) for a 1-wk adjustment period, followed by an increase in 2 chambers to cycling heat stress (HS; 24°C–38°C) for 2 wk. Five ANG and 5 RO heifers were housed at TN, whereas 6 ANG and 5 RO heifers were housed at HS. On day 19, heifers were fitted with jugular catheters. On day 20, heifers were challenged with LPS (0.5 μg/kg BW; 0 h), and blood samples were collected from −2 to 8 h and at 24 h relative to LPS challenge. Serum was analyzed for glucose, insulin, and NEFA concentrations. In addition, feed intake was measured 3 d before and on the day of the challenge. Feed intake decreased over time (P < 0.001) and was decreased in heifers housed at HS compared with heifers housed at TN (P = 0.013). Glucose concentrations before LPS challenge were greater in RO (P = 0.01) than in ANG heifers and greater in TN-housed heifers (P = 0.02) than in HS heifers. Glucose after LPS challenge initially increased before decreasing below baseline concentrations (P < 0.01) in all heifers. In addition, there was a breed by T_a interaction (P < 0.004), such that HS decreased glucose concentrations in ANG heifers compared with ANG heifers housed at TN (P < 0.001), whereas HS did not affect glucose concentrations after LPS challenge in RO heifers (P = 0.941). Nonesterified fatty acid concentrations before LPS challenge were not affected by breed (P = 0.37) or T_a (P = 0.60). Although NEFA concentration after LPS challenge was unaffected by T_a (P = 0.78), there tended to be a breed by T_a interaction (P = 0.07) such that, when housed at HS, RO heifers had greater serum NEFA concentrations after LPS challenge than ANG heifers (P = 0.009). Insulin concentration before LPS challenge was greater in RO heifers than in ANG heifers (P < 0.01). Insulin after LPS challenge increased (P < 0.01), with RO heifers producing a greater insulin response than ANG heifers (P < 0.01). These data suggest that HS decreases the metabolic response of heat-sensitive ANG heifers in response to LPS challenge, thus providing physiological evidence that may explain differences observed in the acute phase response between heat-sensitive ANG and heat-tolerant RO cattle breeds.     

Differential acute phase immune responses by Angus and Romosinuano steers following an endotoxin challenge

Our primary objective of this experiment was to evaluate potential genetic differences between two diverse Bos taurus breeds [Angus (AG) and Romosinuano (RO)] in response to an endotoxin challenge. Eighteen steers (n = 9 steers/breed; 299.4 ± 5.2 kg BW) were acclimated to environmentally controlled chambers maintained at thermoneutrality (19.7 °C) and then fitted with indwelling jugular catheters and rectal temperature (RT) recording devices 1 d before the endotoxin challenge. The next day, blood samples were collected at 30-min intervals from −2 to 8 h, and RT was measured continuously at 1-min intervals throughout the study. At time 0, all steers received an intravenous bolus injection of lipopolysaccharide (LPS; 2.5 μg/kg BW). Serum samples were stored at −80 °C until analyzed for cortisol, proinflammatory cytokines [tumor necrosis factor-alpha (TNF-α), interleukin-1 beta (IL-1β), IL-6, and interferon gamma (IFN-γ)], and acute phase proteins (serum amyloid A, acid soluble protein, ceruloplasmin, and α-acid glycoprotein). Rectal temperatures increased in both breeds within 1 h after LPS, with RO producing a greater increase in RT than AG steers (P < 0.001). Serum cortisol and TNF-α increased (P < 0.01) in both breeds within 1 h after the LPS challenge. For cortisol, an overall breed effect (P < 0.02) was detected, such that AG steers had a higher cortisol response than RO steers. A breed × time interaction (P < 0.01) was observed for TNF-α, such that the response was delayed and extended in the RO steers compared with the AG steers. At 2 and 2.5 h after LPS, TNF-α concentrations were greater (P < 0.03) in RO steers than in AG steers. For IL-1β, a breed × time interaction (P < 0.04) was also observed. At 3 h after LPS, IL-1β concentrations were greater (P < 0.01) in RO steers than in AG steers. Serum IL-6 and IFN-γ increased (P < 0.01) in a similar manner in both groups after the LPS challenge. These data show differences in the innate immune response between two diverse Bos taurus breeds which may provide insight about differences observed in productivity, heat tolerance, disease resistance, and longevity among cattle breeds.     

Variability in tumor necrosis factor-α, nitric oxide,and xanthine oxidase responses to endotoxin challenge in heifers: Effect of estrous cycle stage

The severity of host response to some disease agents differs between sexes and this dimorphism has been attributed to the immunomodulating effects of steroid hormones. Our objective was to determine in heifers whether the phase of estrous cycle affected immune response mediators after endotoxin challenge (LPS, 2.5 μg/kg BW, i.v.). Sixteen beef heifers (426 ± 9 kg) were reproductively synchronized with the two-injection protocol of dinoprost tromethamine (Lutalyse^®, Pfizer) to establish diestrus and estrus stages of the estrous cycle. Heifers were challenged with LPS on day 3 (E, estrus; n = 8) or day 10 (D, diestrus, n = 8) after the last i.m. injection of Lutalyse^®. In all heifers, plasma concentrations of tumor necrosis factor-α (TNF-α) peaked 2 h after LPS treatment (P < 0.01) and returned to basal level by 7 h. However, the integrated TNF-α response (area under the time × concentration curve, AUC) was greater in E than in D (P < 0.05). Plasma concentrations of nitrate + nitrite (NO_x, an estimate of NO production) increased (P < 0.01) in all heifers at 7 and 24 h after LPS; plasma NO_x AUC after LPS was greater in E than D (P < 0.01). Plasma xanthine oxidase activity (XO, a mediator of superoxide production) responses were also greater in E than D (P < 0.05). A companion LPS challenge study in steers validated that the protocol for and use of Lutalyse^® did not affect any of the immune parameters studied in heifers in response to LPS. Results indicate that the underlying physiological attributes of the estrus and diestrus phases of the estrous cycle constitute a major source of variability in the magnitude of proinflammatory response to bacterial toxins like LPS.     

Temporal pattern and effect of sex on lipopolysaccharide-induced stress hormone and cytokine response in pigs

The temporal pattern and sex effect of immune and stress hormone responses to a lipopolysaccharide (LPS) challenge were assessed using a pig model. Secretion of the pro-inflammatory cytokines tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-6 increased in a time-dependent manner following LPS infusion. There was also a time-dependent increase in secretion of the stress-related hormones cortisol, epinephrine (E), and norepinephrine (NE) following LPS, with peak concentrations attained within 30 min. The magnitude of the TNF-α and IL-1β responses were both positively associated (P < 0.05) with the magnitude of cortisol response following LPS, whereas serum IL-1β and IL-6 were positively correlated with the magnitude of E and NE responses following LPS. Acute-phase protein production was also time-dependently increased following LPS. The concentration of immune cells in circulation was decreased (P < 0.05) at 5.5 h post-LPS and negatively correlated with pro-inflammatory cytokine production. By 24 h post-LPS, immune cell counts increased (P < 0.05) and were positively associated with both pro-inflammatory cytokine and stress hormone production. The amplitude of pro-inflammatory cytokine response following LPS was affected (P < 0.05) by sex classification; however, the magnitude of elevated cytokine concentrations was not. The magnitude of the NE response, but not of the E and cortisol responses, to LPS was influenced by sex (P < 0.05). Similar to the pro-inflammatory cytokines, the magnitude of exposure to the stress hormones following LPS was not influenced by sex. The production of serum amyloid A (SAA) was influenced by sex, with barrows producing more SAA than gilts at 24 h post-LPS (P < 0.05). Collectively, these results demonstrate sex-specific, concomitant temporal changes in innate immune- and stress-related hormones.     

Metabolic adaptations to heat stress in growing cattle

To differentiate between the effects of heat stress (HS) and decreased dry matter intake (DMI) on physiological and metabolic variables in growing beef cattle, we conducted an experiment in which a thermoneutral (TN) control group (n = 6) was pair fed (PF) to match nutrient intake with heat-stressed Holstein bull calves (n = 6). Bulls (4 to 5 mo old, 135 kg body weight [BW]) housed in climate-controlled chambers were subjected to 2 experimental periods (P): (1) TN (18 °C to 20 °C) and ad libitum intake for 9 d, and (2) HS (cyclical daily temperatures ranging from 29.4 °C to 40.0 °C) and ad libitum intake or PF (in TN conditions) for 9 d. During each period, blood was collected daily and all calves were subjected to an intravenous insulin tolerance test (ITT) on day 7 and a glucose tolerance test (GTT) on day 8. Heat stress reduced (12%) DMI and by design, PF calves had similar nutrient intake reductions. During P1, BW gain was similar between environments and averaged 1.25 kg/d, and both HS and PF reduced (P < 0.01) average daily gain (-0.09 kg/d) during P2. Compared to PF, HS decreased (P < 0.05) basal circulating glucose concentrations (7%) and tended (P < 0.07) to increase (30%) plasma insulin concentrations, but neither HS nor PF altered plasma nonesterified fatty acid concentrations. Although there were no treatment differences in P2, both HS and PF increased (P < 0.05) plasma urea nitrogen concentrations (75%) compared with P1. In contrast to P1, both HS and PF had increased (16%) glucose disposal, but compared with PF, HS calves had a greater (67%; P < 0.05) insulin response to the GTT. Neither period nor environment acutely affected insulin action, but during P2, calves in both environments tended (P = 0.11) to have a blunted overall glucose response to the ITT. Independent of reduced nutrient intake, HS alters post-absorptive carbohydrate (basal and stimulated) metabolism, characterized primarily by increased basal insulin concentrations and insulin response to a GTT. However, HS-induced reduction in feed intake appears to fully explain decreased average daily gain in Holstein bull calves.     

Effect of heat stress and feeding management on growth performance and physiological responses of finishing pigs

This study aimed to determine whether pig responses to heat stress (HS) were directly due to heat exposure (regardless of feeding level and pattern) or were indirectly due to the reduction of feed intake (FI) and to determine if increasing feeding frequency (splitting heat increments) can improve pig response to HS. A total of 48 pigs (66.1 ± 1.7 kg) were allocated to four groups in three replicates. After 7 d in thermoneutral (TN) conditions (22 °C; period 1 [P1; day −7 to −1]), pigs were placed in either TN or HS (32 °C) conditions for 20 d (period 2 [P2; day 0 to 19]). The diet was provided either ad libitum (AL; 2 distributions/d) or pair-fed (PF8; 8 distributions/d) using HS–AL pigs as the reference group. Thus, the four experimental groups were TN–AL, HS–AL, TN–PF8, and HS–PF8. The daily ration of PF8 pigs was distributed at every 90-min intervals from 0900 to 1930 hours. Data were analyzed using the PROC MIXED procedure with replicate (n = 3), experimental group (n = 4), and their interactions as fixed effects, and the REPEATED statement was used for repeated measures data. Pigs had a similar average daily feed intake (ADFI) during P1 (P > 0.05). In P2, HS–AL and PF8 pigs had lower ADFI (−19%), average daily gain (−25%), and final body weight (−6.1 kg) than TN–AL pigs (P < 0.01). TN–AL pigs had thicker backfat than TN–PF8 pigs (P < 0.05), while the HS pigs had intermediate results. HS pigs had a higher perirenal fat percentage based on the contrast analysis between PF8 pigs (P < 0.05). Thermoregulatory responses of pigs increased with HS exposure but did not differ between HS or between TN groups (P > 0.05). For TN pigs, variation in muscle temperature (T_muscle) depended on feeding and physical activity, while for HS pigs, T_muscle gradually increased throughout the day. The T_muscle of PF8 pigs increased with each additional meal but plateaued earlier for HS–PF8 than TN–PF8 pigs; an increase in T_muscle per meal was also lower in HS–PF8 than TN–PF8 (P < 0.05). Exposure to HS decreased plasma T3 and T4 (P < 0.05) and increased plasma creatinine (P < 0.05). Between the PF8 groups, HS pigs also had a transient increase in plasma insulin on day 8 (P < 0.05). The effect of HS on FI decreased the growth rate of pigs but there are heat-induced effects, such as altered physiological responses, which might explain the direct HS effects seen in other literature especially in terms of increased adiposity. The increased feed provision frequency in the present study did not improve the HS response of pigs.     

Rapamycin administration during an acute heat stress challenge in growing pigs

Study objectives were to determine the effects of rapamycin (Rapa) on biomarkers of metabolism and inflammation during acute heat stress (HS) in growing pigs. Crossbred barrows (n = 32; 63.5 ± 7.2 kg body weight [BW]) were blocked by initial BW and randomly assigned to 1 of 4 environmental-therapeutic treatments: 1) thermoneutral (TN) control (n = 8; TNCon), 2) TN and Rapa (n = 8; TNRapa), 3) HS control (n = 8; HSCon), or 4) HS and Rapa (n = 8; HSRapa). Following 6 d of acclimation to individual pens, pigs were enrolled in two experimental periods (P). During P1 (10 d), pigs were fed ad libitum and housed in TN conditions (21.3 ± 0.2°C). During P2 (24 h), HSCon and HSRapa pigs were exposed to constant HS (35.5 ± 0.4°C), while TNCon and TNRapa pigs remained in TN conditions. Rapamycin (0.15 mg/kg BW) was orally administered twice daily (0700 and 1800 hours) during both P1 and P2. HS increased rectal temperature and respiration rate compared to TN treatments (1.3°C and 87 breaths/min, respectively; P < 0.01). Feed intake (FI) markedly decreased in HS relative to TN treatments (64%; P < 0.01). Additionally, pigs exposed to HS lost BW (4 kg; P < 0.01), while TN pigs gained BW (0.7 kg; P < 0.01). Despite marked changes in phenotypic parameters caused by HS, circulating glucose and blood urea nitrogen did not differ among treatments (P > 0.10). However, the insulin:FI increased in HS relative to TN treatments (P = 0.04). Plasma nonesterified fatty acids (NEFA) increased in HS relative to TN treatments; although this difference was driven by increased NEFA in HSCon compared to TN and HSRapa pigs (P < 0.01). Overall, circulating white blood cells, lymphocytes, and monocytes decreased in HS compared to TN pigs (19%, 23%, and 33%, respectively; P ≤ 0.05). However, circulating neutrophils were similar across treatments (P > 0.31). The neutrophil-to-lymphocyte ratio (NLR) was increased in HS relative to TN pigs (P = 0.02); however, a tendency for reduced NLR was observed in HSRapa compared to HSCon pigs (21%; P = 0.06). Plasma C-reactive protein tended to differ across treatments (P = 0.06) and was increased in HSRapa relative to HSCon pigs (46%; P = 0.03). Circulating haptoglobin was similar between groups. In summary, pigs exposed to HS had altered phenotypic, metabolic, and leukocyte responses; however, Rapa administration had limited impact on outcomes measured herein.     

Serum Lipid Modification Related to Exercise and Polyunsaturated Fatty Acid Supplementation in Jumpers and Thoroughbred Horses

The importance of polyunsaturated fatty acids (PUFAs) within the different biological functions of animals has been widely recognized. In this study, exercise and PUFAs supplementation effects on serum triglycerides, total cholesterol, and nonesterified fatty acids (NEFAs) concentration were evaluated in athletic horses. Two sport horse types (10 Italian saddle jumpers and 10 Thoroughbreds) were equally divided into two groups. Jumpers and Thoroughbred experimental groups (A_J and A_T) received 4-week PUFAs supplementation and control groups (B_J and B_T) received no dietary supplement. Before starting the PUFAs supplementation (T0) and at the end of the experimental period (T4), horses were subjected to simulated events. From each subject, blood samples were collected every 7 days at rest, before and after the first test (T0_R and T0_PE), and before and after the second test (T4_R and T4_PE). Higher triglycerides and NEFA concentrations at T0_PE and T4_PE than T0_R and T4_R in both groups were found as a result of exercise (P < .005), but lower triglycerides and NEFA concentrations at T4_PE in group A_J than group B_J (P < .05) and in group A_T (P < .005) than group B_T were found as a result of PUFAs supplementation. Effects of PUFAs supplementation was highlighted by the statistically significant lower triglycerides and NEFA concentrations found at T4_PE than T0_PE in groups A_J (P < .05) and A_T (triglycerides: P < .05; NEFAs: P < .0001).     

Relationships between feed efficiency and puberty in Bos taurus and Bos indicus-influenced replacement beef heifers

The objective of this experiment was to investigate the relationship between residual feed intake (RFI) and parameters associated with reproductive efficiency in growing beef heifers. One hundred and seventy-nine replacement beef heifers (Bos taurus and Bos indicus-influenced) were enrolled in a retrospective cohort design. Heifers were assigned to a 70-d feed efficiency test, and results were utilized to retrospectively classify heifers into low (n = 51), medium (n = 66), or high (n = 62) RFI groups based on their individual RFI values. Blood samples were collected weekly throughout the feed efficiency test and breeding season, which were analyzed for plasma concentration of progesterone to determine age at puberty (PUB). By design, residual feed intake differed among RFI groups where high (1.21 ± 0.08 kg/d) had greater (P < 0.01) RFI than medium (0.00 ± 0.08 kg/d) and low RFI groups (–1.49 ± 0.09 kg/d), and medium had greater (P < 0.01) RFI than low RFI heifers. Yet, no differences were observed between breed types for RFI (P = 0.53). Average daily gain (ADG) differed between breed types where Bos taurus heifers had greater ADG (P = 0.02) than B. indicus-influenced heifers. Furthermore, ADG tended (P = 0.08) to differ among RFI groups, where medium RFI heifers tended to have reduced ADG compared with low and high RFI heifers. No differences were determined between breed types for gain-to-feed ratio (G:F; P = 0.20; however, G:F differed among RFI groups and was greater (P < 0.01) in low vs. high, and low vs. medium RFI heifers. The percentage of cycling heifers by the start of the breeding season differed (P = 0.03) by RFI group, where a greater percentage of low RFI heifers were cycling compared with high RFI heifers. A difference was determined on PUB between breed types (P = 0.03), where Bos taurus (393.40 ± 4.64 d) heifers had a reduced PUB compared with B. indicus-influenced (406.90 ± 5.07 d) heifers. In addition, PUB differed by RFI group where low (385.96 ± 6.20 d; P < 0.01) and medium (398.47 ± 5.47 d; P = 0.02) RFI heifers had a reduced PUB compared with High RFI heifers (416.03 ± 5.58 d). In conclusion, more feed efficient heifers attained PUB earlier than less feed efficient heifers. Therefore, selection of heifers for feed efficiency may positively impact reproductive performance of replacement beef heifers.     

Effect of feeding slowly fermentable grains on productive variables and amelioration of heat stress in lactating dairy cows in a sub-tropical summer

Feeding low-fiber and high-energy diets to dairy cows is one approach to ameliorate heat stress (HS) by reducing heat increment (HI) during digestion. However, rapidly and slowly fermentable cereal grains differ in their HI. The aim of this experiment was to quantify if feeding slowly fermentable grains ameliorated the physiological responses to HS and improved milk production (MP) in dairy cows. Holstein-Friesian lactating dairy cows were housed in shaded pens and were fed either a total mixed ration (TMR) plus wheat (TMRW), a TMR plus wheat treated with 2% of a commercial starch-binding agent (TMRB), or a TMR plus corn (TMRC) (n?=?8 cows per diet) during summer in Queensland, Australia. Respiration rate (RR) and panting score (PS) were measured four times a day; rumen temperature (RuT) was recorded every 20 min, and rectal temperature (RT) and milk samples were obtained every 4 days. Cows fed slowly fermentable grains had higher milk production (MP) than cows fed TMRW, and cows fed TMRC had lower RT than those fed TMRW and TMRB (P?<?0.001). Rumen temperature was positively correlated with temperature-humidity index and negatively correlated with MP (P?<?0.05). In summary, feeding TMRC ameliorated HS as indicated by lower RT and improved MP in dairy cows. Milk production was improved with starch-binding agents; however, this was not associated with efficient thermoregulatory responses. Furthermore, determination of RuT enabled the prediction of changes in physiological variables and productive responses due to HS in lactating dairy cows.     

Effects of Lactation and Prenatal Androgenization on the Performance,Carcass Composition,and Longissimus Muscle Sensory Characteristics of Heifers in the Single-Calf Heifer System

Two experiments were conducted to evaluate feedlot performance, lactational characteristics, and carcass composition and quality of heifers and the performance of their calves in a single-calf heifer (SCH) system. In Exp. 1, 13 [10 lactating (L) and 3 nonlactating (NL)] prenatally androgenized (PA) heifers, born to cows implanted with testosterone propionate (TP) and 19 (13 L and 6 NL) control (C) heifers, born to nonimplanted cows, were used. Heifers were calved and the pairs were placed in feedlot pens to evaluate the effects of PA on feedlot performance and lactation. Heifers were fed an 85% concentrate diet and fed to a compositional endpoint of 1.1 cm of subcutaneous fat cover, at which point calves were weaned and heifers slaughtered approximately 12 h later. The NL heifers consumed 17.0% less (P<0.01) dry matter and were 30.8% more (P<0.01) efficient in feed conversion. When calf performance was included, overall feed efficiency of L heifers was 26.9% greater (P<0.05; 0.151 vs 0.119) than that of the NL feedlot heifers. Prenatal androgenization had no effect on heifer performance. Four percent fat-corrected milk yield averaged 7.79 and 5.62 kg/d for PA and C heifers, respectively. The NL heifers had 11.0% greater (P<0.01) marbling score and yield grades were 3.77 and 3.03 (P<0.05) for NL and L heifers, respectively. Livers (P<0.01) and kidneys (P<0.05) as a percentage of shrunk weight were heavier for L heifers than for NL heifers. Two carcasses were classified as hard-boned (C-maturity) and 74% received a USDA Choice grade. The L heifers tended (P<0.10) to have lower taste panel tenderness scores; however, shearforce was similar (P=0.81) for L and NL heifers. In Exp. 2, 24 Angus × Holstein heifers were utilized in the single-calf heifer system, similar to Exp. 1. Calves were weaned from their dam between d 64 and 89 postpartum. Heifers that had their calves early weaned (EW) gained 44.2% faster (P<0.01) and consumed 10.8% less (P<0.05) DM than L heifers. The EW heifers were 60.0% more (P<0.01) efficient than L heifers. However, when calf performance was included with heifer performance, L heifers were 23.7% more (P<0.05) efficient than EW heifers. The EW heifers had 18.9% heavier (P<0.01) hot carcasses than L heifers. Backfat thickness was 1.07 and 0.66 cm (P<0.01) for the EW and L heifers.     

Forage and breed effects on behavior and temperament of pregnant beef heifers

Background

Integration of behavioral observations with traditional selection schemes may lead to enhanced animal well-being and more profitable forage-based cattle production systems. Brahman-influenced (BR; n = 64) and Gelbvieh × Angus (GA; n = 64) heifers consumed either toxic endophyte-infected tall fescue (E+) or one of two nontoxic endophyte-infected tall fescue (NT) cultivars during two yr. Heifers were weighed at midpoint and termination of grazing. Grazing behavior (grazing, resting in the shade, lying, or standing without grazing) was recorded (n = 13 visual observations per yr in June and July) for each pasture. During yr 2, exit velocity (EV) and serum prolactin (PRL) were determined.

Results

Grazing behavior was influenced (P < 0.05) by an interaction between fescue cultivar and breed type. Gelbvieh × Angus heifers assigned to E+ pastures had the lowest percentage of animals grazing and the largest percentage of animals resting in the shade. Brahman-influenced heifers had faster EV (P < 0.001) than GA heifers (0.52 vs. 0.74 ± 0.04 s/m, respectively). Body weight (BW) was affected (P < 0.01) by an interaction of tall fescue cultivar and d, and an interaction of tall fescue cultivar and breed type. Heifers grazing NT pastures were heavier (P < 0.01) than heifers grazing E+ pastures at midpoint and termination. Gelbvieh × Angus heifers grazing NT pastures were heavier (P < 0.01) than GA and BR heifers grazing E+ and BR heifers grazing NT pastures. An interaction of forage cultivar and breed type occurred on serum PRL (P < 0.01).

Conclusion

Collectively fescue cultivar, EV, and concentrations of serum PRL were associated with grazing behavior. Heifers grazing NT pastures were observed to be grazing more than heifers assigned to E+ pastures, regardless of breed type, which may have contributed to changes in BW and average daily gain (ADG) in heifers. Integration of behavioral observations along with traditional selection schemes may lead to enhanced animal well-being and more profitable forage-based cattle production systems.     

Effects of oxytocin,lipopolysaccharide (LPS), and polyunsaturated fatty acids on prostaglandin secretion and gene expression in equine endometrial explant cultures

Increased secretion of prostaglandin F₂α (PGF₂α) within the uterus because of uterine inflammation can cause luteolysis and result in early embryonic loss. Supplementation with polyunsaturated fatty acids (PUFAs) has been shown to influence PG production in many species, although the effects on the mare remain unknown. The present study aimed to determine fatty acid uptake in equine endometrial explants and evaluate their influence on PG secretion and expression of enzymes involved in PG synthesis in vitro. Equine endometrial explants were treated with 100 μM arachidonic acid, eicosapentaenoic acid, or docosahexaenoic acid and then challenged with oxytocin (250 nM) or lipopolysaccharide (LPS; 1 μg/mL). Production of PGF₂α and PG E₂ (PGE₂) was measured, and mRNA expression of enzymes involved in PG synthesis was determined with quantitative real-time PCR. Media concentrations of PGF₂α and PGE₂ were higher (P < 0.0001) from endometrial explants challenged with oxytocin or LPS compared with controls despite which fatty acid was added. Only DHA lowered (P < 0.0001) media concentrations of PGF₂α and PGE₂ from explants. Endometrial explants stimulated with oxytocin had increased expression of PG-endoperoxide synthase 1 (PTGS1; P < 0.02), PG-endoperoxide synthase 2 (PTGS2; P < 0.001), PG F₂α synthase (PGFS; P < 0.01), PG E₂ synthase (PGES; P < 0.01), and phospholipase A₂ (PLA₂; P < 0.005) compared with controls and regardless of fatty acid treatment; whereas stimulation with LPS increased expression of PTGS2 (P < 0.004), PGFS (P < 0.03), PGES (P < 0.01), and PLA₂ (P < 0.01) compared with controls and regardless of fatty acid treatment. Treatment with PUFAs, specifically DHA, can influence PG secretion in vitro through mechanisms other than enzyme expression.     

Progesterone concentration,estradiol pretreatment,and dose of gonadotropin-releasing hormone affect gonadotropin-releasing hormone-mediated luteinizing hormone release in beef heifers

We examined whether progesterone (P₄)-induced suppression of LH release in cattle can be overcome by an increased dose of exogenous gonadotropin-releasing hormone (GnRH) or pretreatment with estradiol (E₂). In Experiment 1, postpubertal Angus-cross heifers (N = 32) had their 2 largest ovarian follicles ablated 5 d after ovulation. Concurrently, these heifers were all given a once-used, intravaginal P₄-releasing insert (CIDR), and they were randomly assigned to be given either prostaglandin F_2α (Low-P₄) or no treatment (High-P₄) at follicle ablation, and 12 h later. Six days after emergence of a new follicular wave, half of the heifers in each group (n = 8) were given either 100 or 200 μg of GnRH i.m. Plasma luteinizing hormone (LH) concentrations were higher in the Low- vs High-P₄ groups, and in heifers given 200 vs 100 μg of GnRH (mean ± SEM 15.4 ± 2.2 vs 9.1 ± 1.2, and 14.8 ± 2.1 vs 9.8 ± 1.4 ng/mL, respectively; P ≤ 0.01). Ovulation rate was higher (P = 0.002) in the Low-P₄ group (15/16) than in the High-P₄ group (6/16), but it was not affected by GnRH dose (P = 0.4). In Experiment 2, heifers (n = 22) were treated similarly, except that 5.5 d after wave emergence, half of the heifers in each group were further allocated to be given either 0.25 mg estradiol benzoate i.m. or no treatment, and 8 h later, all heifers were given 100 μg GnRH i.m. Both groups treated with E₂ (Low- and High-P₄) and the Low-P₄ group without E₂ had higher peak plasma LH concentrations compared to the group with high P₄ without E₂ (12.6 ± 1.8, 10.4 ± 1.8, 8.7 ± 1.3, and 3.9 ± 1.2 ng/mL, respectively; (P < 0.04)). However, E₂ pretreatment did not increase ovulation rates in response to GnRH (P = 0.6). In summary, the hypotheses that higher doses of GnRH will be more efficacious in inducing LH release and that exogenous E₂ will increase LH release following treatment with GnRH were supported, but neither significantly increased ovulation rate.     

Effects of increased ambient temperature and supplemental altrenogest before pregnancy establishment in gilts

Heat stress (HS) mitigation strategies are critically needed to combat the substantial economic effects on animal agriculture. The manifestations of seasonal infertility include delayed puberty onset, reduced conception rates, decreased litter size, and increased wean to estrus interval. To assess the effects of HS during early gestation and evaluate the benefit of supplemental altrenogest (ALT) as a mitigation strategy, 30 crossbred postpubertal gilts (157 ± 11 kg body weight) were subjected to estrous synchronization via 14 d oral administration of ALT. Artificial insemination during estrus was performed, and gilts were then placed into one of four treatment groups: HS (35 ± 1 °C for 12 h/31.60 ± 1 °C for 12 h) with (HSALT, n = 7) or without (HSCON, n = 7) 15 mg/d ALT supplementation or thermal neutral (TN; 20 ± 1 °C) conditions with (TNALT, n = 8) or without (TNCON, n = 8) 15 mg/d ALT supplementation until 12 d post-estrus (dpe). Administrating ALT occurred at 0600 hours from 3 to 12 dpe, and rectal temperatures (T_R) and respiration rates (RR) were recorded. Blood was collected via jugular venipuncture on 0, 4, 8, and 12 dpe. Gilts were euthanized humanely at 12 dpe followed by the collection of ovarian tissue, and uterine flushing for conceptus collection. In HS compared with TN gilts, RR and T_R were increased (P < 0.01) but unaffected by ALT supplementation. Feed intake was reduced (P < 0.01) by HS but unaltered by the ALT treatment. Corpora lutea (CL) weight was reduced (P < 0.01) in HSCON gilts when compared with TNCON and HSALT gilts despite progesterone concentrations in serum and luteal tissue not being affected by treatment (P ≥ 0.10). CL diameter was reduced (P ≤ 0.05) in HSALT gilts compared with other treatments. Interleukin-1β (IL1B) uterine flush concentration was not affected (P > 0.20) by environment or ALT supplementation, although moderate (P = 0.06) interaction between environment and ALT existed, as IL1B concentration in TNALT was increased (P = 0.03) compared with TNCON gilts. While environment did not affect conceptus development (P = 0.90), ALT supplementation advanced conceptus elongation (P < 0.01). Collectively, these data demonstrate that HS may affect luteal development before pregnancy establishment, and ALT increases conceptus elongation by 12 dpe.     

Effects of road transportation on metabolic and immunological responses in Holstein heifers

This study examined the effects of road transportation on metabolic and immunological responses in dairy heifers. Twenty Holstein heifers in early pregnancy were divided into non‐transported (NT; n = 7) and transported (T; n = 13) groups. Blood was collected before transportation (BT), immediately after transportation for 100 km (T1) and 200 km (T2), and 24 h after transportation (AT). The T heifers had higher (P < 0.05) blood cortisol and non‐esterified fatty acid concentrations after T1 and T2 than did NT heifers. By contrast, the T heifers had lower (P < 0.05) serum triglyceride concentrations after T1 and T2 than had the NT heifers. The serum cortisol and triglyceride concentrations returned (P > 0.05) to the BT concentrations at 24 h AT in the T heifers. The granulocyte‐to‐lymphocyte ratio and the percentage of monocytes were higher (P < 0.05) after T2 in the T heifers than in the NT heifers, suggesting that transportation stress increased the numbers of innate immune cells. T heifers had higher (P < 0.01) plasma haptoglobin concentrations than NT heifers 24 h AT. In conclusion, transportation increased cortisol secretion and was correlated with increased metabolic responses and up‐regulation of peripheral innate immune cells in dairy heifers.     

Yeast mixture of liquid beer and cassava pulp with rice straw for the growth of dairy heifers

This study was conducted to determine the effects of mixtures of liquid brewer’s yeast (LBY) and cassava pulp (CVP) with rice straw (RS) on feed intake, digestibility, rumen fermentation, and growth of dairy heifers. Sixteen Holstein crossbred heifers (13.8?±?1.6 months old, 210?±?23 kg body weight (BW)) were randomly allocated to four feeding treatments with four replications, which were 0:0:100 (RS), 0:70:30 (0%LBY), 20:50:30 (20%LBY), and 50:20:30 (50%LBY), respectively, for LBY/CVP/RS on a fresh matter basis. The heifers were offered conventional concentrate at 1.5% initial body weight daily and fed the treatment diets ad libitum. Average daily gain and feed intake were not significantly different among the treatments. The heifers fed 50%LBY had the highest crude protein (CP) intake and DM, OM, and CP digestibility (P?<?0.05). The ruminal pH did not differ significantly among treatments, while NH₃-N was the highest (P?<?0.05) in 50%LBY. Total volatile fatty acid (VFA) concentrations and the molar proportion of each VFA were not significantly different among the treatments. Blood urea nitrogen concentrations of 50%LBY were the highest among the treatments (P?<?0.05). The results indicated that 50%LBY improved CP digestibility.     

Impact of seasonal thermal stress on physiological and blood biochemical parameters in pigs under different dietary energy levels

The present study was formulated to find out the status of important season related thermal stress biomarkers of pure-bred (Hampshire) and crossbred (50% Hampshire × 50% local) pigs under the agro-climatic condition of Assam State, India. The experiment was also aimed to study the role of different level of energy ration (110, 100, and 90% energy of NRC feeding standard for pig) in variation of physiological and biochemical parameters in two genetic groups of pigs in different seasons. The metabolizable energy value were 3260, 2936.5, and 3585.8 kcal/kg in grower ration and 3260.2, 2936.6, and 3587 kcal/kg in finisher ration for normal energy (NE), low energy (LE) and high energy (HE), respectively. Both the genetic group of animals were housed separately under intensive system of management. Each pen was measuring 10′ × 12′ along with an outer enclosure. Six weaned piglets (almost similar body weight of average 10.55 kg) of each group were kept in a separate pen. However, after attainment of 35 kg body weight, the animals of a group were divided in two pens of three animals each. The present experiment indicated that average ambient temperature during summer months (27.33–29.51 °C) was above the comfort zone for pigs (22 °C). The significantly (P?<?0.01) higher relative humidity (RH) (%) was recorded in outdoor environment (87.26–91.10%) and in the morning time (86.60–91.10%). The temperature humidity index (THI) during the study period was found to be indicative of thermal stress to the experimental animals during summer (79.55–82.56). Physiological parameters viz., respiration rate (RR) and rectal temperature (RT) were significantly (P?<?0.01) higher in summer season (43.75–72.12 breaths/min. and 102.29–103.23 °F) and non-significantly higher values were recorded in Hampshire pigs. It was also found that the significantly (P?<?0.01) lower RR as well as RT was recorded in the pigs fed with high energy (HE) ration during summer season. Serum triiodothyronine (T₃) and thyroxine (T₄) concentrations were significantly (P?<?0.01) lower during summer, while both the genetic groups showed significantly (P?<?0.01) higher concentration of serum cortisol during summer season. It was also observed that thyroid hormone and cortisol concentrations were maintained in groups of pig fed vegetable oil incorporated HE diet during summer. From the present study, it is found that the increasing the energy level of the ration might be helpful to minimize the effects of thermal stress during summer.     

Effect of season and breed group on the follicular population and cyclicity of heifers under tropical conditions

The aim was to determine the effect of season and breed group on follicular population, and presence and size of CL of heifers under tropical conditions. The seasons were hot-dry (March–June), hot-humid (July–October), and fresh-humid (November–February). Thirty Zebu (Brahman) and 38 F1 (Simmental?×?Brahman) heifers were used. Five evaluations were made in each season, at intervals of 7 days, to assess ovarian activity by ultrasound. Follicles were classified as small (≤4 mm), middle (4.1–8 mm), and large (≥8.1 mm) sizes, and also the size of CL, when present, was measured. Data were analyzed using analysis of variance and logistic regression procedures. Mean number of small follicles was 11.6?±?2.3 with no effect of season, breed group, or their interaction (P?>?0.05). Mean number of middle follicles was influenced by season and breed group; the highest average was found in the fresh-humid season (4.0?±?0.2) and in F1 heifers (3.6?±?0.2; P?<?0.05). The highest mean number of large follicles was in the hot-humid season (1.4?±?0.1; P?<?0.05). The highest maximum follicle diameter (MFD) mean was registered in the hot-humid season (1.3 mm; P?<?0.05) and the lowest proportion of heifers with CL occurred in fresh-humid season (33.3%; P?<?0.05). No effect of season, breed group, and interaction on the maximum diameter of the CL was found. In conclusion, season was a very important source of variation. Heifers in the hot-humid season had the largest follicles and MFD, and better cyclicity.

     

Hematologic and biochemical reference intervals for specific pathogen free 6-week-old Hampshire-Yorkshire crossbred pigs

Background

Heifers not used as breeding stock are often implanted with steroids to increase growth efficiency thereby altering hormone profiles and potentially changing the environment in which ovarian follicles develop. Because bovine granulosa cell culture is a commonly used technique and often bovine ovaries are collected from abattoirs with no record of implant status, the objective of this study was to determine if the presence of an implant during bovine granulosa cell development impacts follicle stimulating hormone-regulated steroidogenic enzyme expression. Paired ovaries were collected from 16 feedlot heifers subjected to 1 of 3 treatments: non-implanted (n?=?5), Revalor 200 for 28 d (n?=?5), or Revalor 200 for 84 d (n?=?6). Small follicle (1 to 5 mm) granulosa cells were isolated from each pair and incubated with phosphate buffered saline (n?=?16) or 100 ng/mL follicle stimulating hormone (n?=?16) for 24 h.

Results

Granulosa cells of implanted heifers treated with follicle stimulating hormone produced medium concentrations of progesterone similar (P?=?0.22) to non-implanted heifers, while medium estradiol concentrations were increased (P?<?0.10) at 28 and 84 d compared to non-implanted heifers indicating efficacy of treatment. Additionally, real-time PCR analysis in response to follicle stimulating hormone treatment demonstrated a decrease in steroidogenic acute regulatory protein (P?=?0.05) mRNA expression in heifers implanted for 84 d and an increase in P450 side chain cleavage mRNA in granulosa cells of heifers implanted for 28 (P?<?0.10) or 84 d (P?<?0.05) compared to non-implanted females. However, no difference in expression of 3-beta-hydroxysteroid dehydrogenase (P?=?0.57) and aromatase (P?=?0.23) were demonstrated in implanted or non-implanted heifers.

Conclusions

These results indicate follicles which develop in the presence of high concentrations of androgenic and estrogenic steroids via an implant tend to demonstrate an altered capacity to respond to follicle stimulating hormone stimulation. Thus, efforts should be made to avoid the use of implanted heifers to study steroidogenesis in small follicle granulosa cell culture systems.