Effect of fat supplementation during transition period on plasma leptin and non‐esterified fatty acid concentrations in Holstein cows

The objective of this experiment was to investigate the effect of fat supplementation during the transition period on pre and postpartum body weight (BW), body condition score (BCS), non‐esterified fatty acids (NEFA), glucose and leptin concentrations in Holstein cows. Holstein cows (n = 15) received a low fat diet (LF; 1.61 Mcal net energy for lactation (NEL)/kg of dry matter [DM]), moderate fat diet (MF; 1.68 Mcal NEL/kg DM) or a high fat diet (HF; 1.74 Mcal NEL/kg DM) for 4 weeks prior to calving. All cows were fed similar lactation diets ad libitum (1.74 Mcal NEL/kg DM) for 30 days after calving. Increasing diet energy density during transition period had no effect on prepartum DMI, BCS, BW, glucose and NEFA concentrations (P > 0.05); but leptin concentrations and energy balance (EB) were affected by treatments (P < 0.05). Animals fed HF had less plasma leptin prepartum. After parturition, BW, milk production, milk fat, protein, urea nitrogen and plasma glucose concentrations were affected by prepartum diets (P < 0.05). Fat supplementation prepartum did not affect postpartum NEFA. In conclusion, prepartum fat supplementation decreased leptin concentration prepartum.     

Effects of body composition, pre- and postpartum energy intake and stage of production of energy utilization by beef cows

Mature Charolais x Angus cows (n = 128) were adjusted to a body condition score (BCS) of 3 (1 = very thin, 3 = moderate, 5 = very fat) between 130 and 190 d of gestation. When cows averaged 190 d of gestation, they were assigned randomly to a maintenance energy diet (ME) or to a diet very low in energy (LE). Cows were allotted within these prepartum (PRP) diets to a high-energy (HE) or LE diet at parturition. At 30 d postpartum (PP), cows were allotted to four treatments: a) slaughter at 0 (n = 32) or b) 48 h after calf removal (n = 32), c) cows whose calves were early weaned at 30 d PP (n = 32) or d) normally weaned at 205 d PP (n = 32). Low energy PRP intake reduced (P less than .01) BCS, cow weight, total empty body lipid (TEBL), body energy (BE) and daily predicted maintenance energy (PME)/W.75 by parturition. Pre- and postpartum energy intake combined to affect (P less than .10) these same factors in a similar manner at 30 d PP. From 30 to 60 d PP, early weaning reduced (P less than .05) PME/W.75. Cow BCS at 190 d of gestation had little effect (P greater than .10) on PME/W.75 or PME/Mcal of BE. Body condition score at parturition, however, affected (P less than .05) delta BCS, delta BE and PME/Mcal of BE by 30 and 60 d PP, with thinner cows losing less condition and requiring more PME/Mcal of BE. Cow BCS had a similar effect from 30 to 60 d PP. Total daily PME was greater for the fat cows during both the PRP and PP periods. Body composition, PRP and PP energy intake and early weaning affect energy requirements and energetic efficiency of beef cows.     

Energy metabolism in lactating beef heifers

To obtain measurements of energy balance in lactating beef cows, respiration calorimetry and digestion trials were conducted using seven lactating (613 kg BW) and three nonlactating (598 kg BW) Hereford x Angus heifers fed a pelleted 75% alfalfa:25% concentrate diet. Five measurements of energy balance were obtained at 6- to 7-wk intervals beginning 6 to 10 wk postpartum in lactating heifers and at 6-wk intervals in nonlactating heifers. Milk yield was measured using a combination of weigh-suckle-weigh and machine milking to adapt heifers to milking by machine without the use of oxytocin. Heifers were milked only by machine during measurements of energy balance. Weekly milk yield averages ranged from 8.2 kg/d at wk 5 postpartum to 3.2 kg/d at wk 32 postpartum. When scaled to BW(.75), the regression of NE1 on ME intake and the regression of ME intake on NE1 were remarkably similar to previously published regressions for measurements obtained from lactating Holstein-Friesian cows. The average daily maintenance energy requirement from these regressions was 503 kJ ME/kg BW(.75), a value similar to the average value reported previously for lactating Holstein-Friesian cows (488 kJ/kg (BW.75)). This is in contrast to numerous published comparisons of the maintenance requirements of cattle breed types in the nonlactating state and current NRC standards for estimating maintenance energy requirements of beef and dairy cattle. The results of the present study suggest that when expressed on the basis of BW(.75) the efficiency of utilization of incremental ME above maintenance for milk and tissue energy (i.e., NE1) is similar among lactating Hereford x Angus heifers and lactating Holstein-Friesian cows. The breeds differ in terms of their propensity for milk yield and the resulting partition of ME between milk synthesis and tissue energy retention.     

Body condition score at parturition and postpartum supplemental fat effects on cow and calf performance

Three-year-old Angus x Gelbvieh beef cows nutritionally managed to achieve a BCS of 4 +/- 0.07 (479.3 +/- 36.3 kg of BW) or 6 +/- 0.07 (579.6 +/- 53.1 kg of BW) at parturition were used in a 2-yr experiment (n = 36/yr) to determine the effects of prepartum energy balance and postpartum lipid supplementation on cow and calf performance. Beginning 3 d postpartum, cows within each BCS were assigned randomly to be fed hay and a low-fat control supplement or supplements with either high-linoleate cracked safflower seeds or high-oleate cracked safflower seeds until d 60 of lactation. Diets were formulated to be isonitrogenous and isocaloric, and safflower seed supplements were provided to achieve 5% of DMI as fat. Ultrasonic 12th rib fat and LM area were lower (P < 0.001) for cows in BCS 4 compared with BCS 6 cows throughout the study. Cows in BCS 4 at parturition maintained (P = 0.02) condition over the course of the study, whereas cows in BCS 6 lost condition. No differences (P = 0.44 to 0.71) were detected for milk yield, milk energy, milk fat percentage, or milk lactose percentage because of BCS; however, milk protein percentage was less (P = 0.03) for BCS 4 cows. First-service conception rates did not differ (P = 0.22) because of BCS at parturition, but overall pregnancy rate was greater (P = 0.02) in BCS 6 cows. No differences (P = 0.48 to 0.83) were detected in calf birth weight or ADG because of BCS at parturition. Dietary lipid supplementation did not influence (P = 0.23 to 0.96) cow BW change, BCS change, 12th rib fat, LM area, milk yield, milk energy, milk fat percentage, milk lactose percentage, first service conception, overall pregnancy rates, or calf performance. Although cows in BCS of 4 at parturition seemed capable of maintaining BCS during lactation, the overall decrease in pregnancy rate indicates cows should be managed to achieve a BCS >4 before parturition to improve reproductive success.     

Efficacy of using a combination of rendered protein products as an undegradable intake protein supplement for lactating, winter-calving, beef cows fed bromegrass hay

Seventy-two (36 in each of two consecutive years) lactating, British-crossbred cows (609 +/- 19 kg) were used to evaluate effects of feeding a feather meal-blood meal combination on performance by beef cows fed grass hay. Bromegrass hay (9.6% CP, DM basis) was offered ad libitum and intake was measured daily in individual Calan electronic headgates. Acclimation to Calan gates began approximately 20 d after parturition, and treatments were initiated 21 d later. Cows were assigned randomly to one of four treatments (DM basis) for 60 d: 1) nonsupplemented control (CON), 2) energy control (ENG; 790 g/d; 100% beet pulp), 3) degradable intake protein (DIP; 870 g/d; 22% beet pulp and 78% sunflower meal), or 4) undegradable intake protein (UIP; 800 g/d; 62.5% sunflower meal, 30% hydrolyzed feather meal, and 7.5% blood meal). Net energy concentrations of supplements were formulated to provide similar NE(m) intakes (1.36 Mcal/d). The DIP and UIP supplements were calculated to supply similar amounts of DIP (168 g/d) and to supply 64 and 224 g/d of UIP, respectively. Forage DMI (kg/d) decreased in supplemented vs. nonsupplemented (P = 0.03) and DIP vs. UIP (P = 0.001); however, when expressed as a percentage of BW, forage DMI was not different (P = 0.23). Supplemented cows tended (P = 0.17) to lose less BW than CON. Body condition change was not affected (P = 0.60) by postpartum supplementation. No differences were noted in milk production (P = 0.29) or in calf gain during the supplementation period (P = 0.74). Circulating insulin concentrations were not affected by treatment (P = 0.42). In addition, supplementation did not affect circulating concentrations of NEFA (P = 0.18) or plasma urea nitrogen (P = 0.38). Results of the current study indicate that supplementation had little effect on BW, BCS, milk production, or calf BW when a moderate-quality forage (9.6% CP) was fed to postpartum, winter-calving cows in optimal body condition (BCS > 5). Supplemental UIP did not enhance cow performance during lactation. Forage UIP and microbial protein supply were adequate to meet the metabolizable protein requirements of lactating beef cows under the conditions of this study.     

Cow/calf preweaning efficiency of Nellore and Bos taurus x Bos indicus crosses

The objectives of this study were to determine if percentage Bos taurus (0 or 50%) of the cow had an effect on ME requirements and milk production, and to compare cow/calf efficiency among 3 mating systems. Metabolizable energy requirements were estimated during a feeding trial that encompassed a gestation and lactation feeding trial for each of 2 groups of cows. Cows were 0 or 50% Bos taurus (100 or 50% Nellore) breed type: Nellore cows (NL; n = 10) mated to Nellore bulls, NL cows (n = 9) mated to Angus bulls, Angus x Nellore (ANL; n = 10) and Simmental x Nellore (SNL; n = 10) cows mated to Canchim (5/8 Charolais 3/8 Zebu) bulls. Cows were individually fed a total mixed diet that contained 11.3% CP and 2.23 Mcal of ME/kg of DM. At 14-d intervals, cows and calves were weighed and the amount of DM was adjusted to keep shrunk BW and BCS of cows constant. Beginning at 38 d of age, corn silage was available to calves ad libitum. Milk production at 42, 98, 126, and 180 d postpartum was measured using the weigh-suckle-weigh technique. At 190 d of age, calves were slaughtered and body composition estimated using 9-10-11th-rib section to obtain energy deposition. Regression of BW change on daily ME intake (MEI) was used to estimate MEI at zero BW change. Increase in percentage Bos taurus had a significant effect on daily ME requirements (Mcal/d) during pregnancy (P < 0.01) and lactation (P < 0.01). Percentage Bos taurus had a positive linear effect on maintenance requirements of pregnant (P = 0.07) and lactating (P < 0.01) cows; during pregnancy, the ME requirements were 91 and 86% of those in lactation (131 +/- 3.5 vs. 145 +/- 3.4 Mcal x kg(-0.75) x d(-1)) for the 0 and 50% B. taurus groups, respectively. The 50% B. taurus cows, ANL and SNL, suckling crossbred calves had greater total MEI (4,319 +/- 61 Mcal; P < 0.01) than 0% B. taurus cows suckling NL (3,484 +/- 86 Mcal) or ANL calves (3,600 +/- 91 Mcal). The 0% B. taurus cows suckling ANL calves were more efficient (45.3 +/- 1.6 g/Mcal; P = 0.03) than straightbred NL (35.1 +/- 1.5 g/Mcal) and ANL or SNL pairs (41.0 +/- 1.0 g/Mcal). Under the conditions of this study, crossbreeding improved cow/ calf efficiency and showed an advantage for cows that have lower energy requirements.     

Prediction of empty body composition of double-muscled beef cows

Twenty-four nonlactating and nonpregnant Belgian Blue double-muscled cows, with diverging parities (one to seven), body conditions and body weights (436 to 903 kg), were used to investigate empty body (EB) composition. Direct measurements of EB composition, such as water, fat, protein, ash and energy, were carried out after slaughter. EB weight (EBW) averaged 624.7 kg and consisted of 393.3 kg water, 122.3 kg protein, 84.5 kg fat and 24.6 kg ash and was characterized by an energy content of 6158 MJ. Relationships between body weight (BW), body condition score (BCS), chest girth, dressing percentage, carcass grading score, EBW, rib-cut components and EB composition were determined. Significant regression equations (P<0.001) with a coefficient of determination (R²) of more than 0.9 were obtained between BW or BW and BCS and EB water, EB fat and EB energy. The prediction of EB ash was less accurate (R²<0.75). The relationship could further be improved by inclusion of carcass characteristics and rib-cut components (R²>0.95). Energy contents of EB lipids and protein amounted to 39.3 and 23.2 MJ/kg. EB protein (197 g/kg) was higher in the present double-muscled cows than reported for non-double-muscled animals, while EB fat (126 g/kg) and EB energy (9.5 MJ/kg) were lower. One BCS unit corresponded with 26.7 kg EB fat (P<0.001; R²=0.659). It can be concluded that simple live animal measurements as BW and BCS can be considered as potentially useful predictors of EB composition in double-muscled cows. Theoretical calculations based on the present observed data indicated that body reserves were lower in Belgian Blue double-muscled cows than in most other breeds. Body reserve tissue may be limited in young primiparous suckling cows so that energy restriction may be detrimental for reproductive performance.     

Effects of induced hypothyroidism on weight gains, lactation, and reproductive performance of primiparous Brahman cows.

Primiparous, spring-calving Brahman cows (BW = 425.0 +/- 13.8 kg, body condition score [BCS] = 5.0 +/- .2 units; SEM) were used to study the effects of thyroid manipulation on weight gain, milk production, and reproduction. Nine cows served as controls. Nine cows were induced to become hypothyroid by daily ingestion of 4 mg/kg BW of 6-n-propyl-2-thiouracil (PTU). Cows were stratified to treatment 1 d after calving based on season of birth, BW, BCS, calf sex, and calf sire. The treatment period lasted for 84 d and was followed by a 56-d posttreatment period. Cow BW, BCS, and calf weight were recorded twice weekly. Milk production was estimated at 14, 28, 56, 84, 98, 112, and 140 d after calving. Weekly blood samples were obtained for analysis of triiodothyronine (T3), thyroxine (T4), and progesterone (P4). Estrus was monitored twice daily with the aid of a fertile bull equipped with a chin ball marker. Hypothyroidism was effectively induced in all PTU cows during the treatment period. The PTU cows gained more (P = .002) weight (54.6 +/- 7.6 kg) and tended (P = .06) to increase body condition (.61 +/- .17 units) more than control cows (15.7 +/- 7.6 kg; .11 +/- .17 units) during the treatment period. Control calves gained at a faster rate (.85 +/- .04 kg/d; P < .01) than PTU calves (.70 +/- .04 kg/d) during the treatment period. Milk production was lower (P < .05) in PTU cows on d 56 and 84. During posttreatment all trends were reversed, and BW, BCS, calf weight, and milk production were similar between the two groups by d 140. Reproductive performance was not affected by induction of hypothyroidism. In conclusion, induction of hypothyroidism was successful in increasing cow weight and BCS gains and suppressing milk production during the treatment period, but these changes were not successful in improving reproductive performance of primiparous Brahman cows.     

Influence of prepartum body condition score change on reproduction in multiparous beef cows calving in moderate body condition.

Multiparous, spring-calving beef cows (n = 250) were used to determine whether large changes in body energy reserves during mid- to late gestation influenced subsequent reproductive performance of cows calving in moderate body condition. In three states, cows were blocked by BW and body condition score (BCS; 1 = emaciated to 9 = obese) then allotted to receive either a high or low plane of nutrition from late summer to early winter over a 3-yr period. This generated an array of BCS by the beginning of the last trimester of pregnancy when cows were grouped by BCS as follows: Group 1, BCS < or = 4; Group 2, BCS of 5 or 6; and Group 3, BCS > or = 7. Each group was managed so that individual cows would calve with a BCS of 5 to 6. At the time of group assignment, mean BW and BCS differed (P < .01) among groups and were 480 kg and 3.6, 541 kg and 5.5, and 594 kg and 7.1 for Groups 1 to 3, respectively. Within 28 d before calving, BW and BCS were similar (P > .20) among groups averaging 555 kg and 5.1. Prepartum BCS changes averaged 1.4, -.4, and -2.0 units for Groups 1 to 3, respectively (P < .01). Cows were managed as a single group after calving in each state. Location effect was significant for the prepartum and postpartum BW and BCS changes but not for postpartum reproductive performance. Significant location x BCS group interactions were found for the 90-d prepartum BW, BCS at calving, and prepartum changes in BW, but were caused by differences in magnitude among locations. The percentage of cows with luteal activity at the start of a subsequent breeding season was not affected (P > .20) by either location or BCS group, and averaged 66%. Mean pregnancy rates at 20, 40, and 60 d of a subsequent breeding season were 55, 76, and 89% for Group 1; 51, 67, and 82% for Group 2; and 64, 79, and 89% for Group 3 (P > .30). Mean days to conception were 89, 87, and 85 for Groups 1 to 3, respectively (P = .70). Neither calf birth weight (x = 38.6 kg) nor adjusted 205-d weight (x = 223.6 kg) were affected by prepartum BW and BCS changes. We conclude that reproductive performance of cows calving in moderate body condition is not influenced by large changes in body energy reserves during the last trimester of pregnancy.     

Energy and protein requirements for maintenance and growth of Boer crossbred kids

Meat production by goats has become an important livestock enterprise in several parts of the world. Nonetheless, energy and protein requirements of meat goats have not been defined thoroughly. The objective of this study was to determine the energy and protein requirements for maintenance and growth of 34 (3/4) Boer x (1/4) Saanen crossbred, intact male kids (20.5 +/- 0.24 kg of initial BW). The baseline group was 7 randomly selected kids, averaging 21.2 +/- 0.36 kg of BW. An intermediate group consisted of 6 randomly selected kids, fed for ad libitum intake, that were slaughtered when they reached an average BW of 28.2 +/- 0.39 kg. The remaining kids (n = 21) were allocated randomly on d 0 to 3 levels of DMI (treatments were ad libitum or restricted to 70 or 40% of the ad libitum intake) within 7 slaughter groups. A slaughter group contained 1 kid from each treatment, and kids were slaughtered when the ad libitum treatment kid reached 35 kg of BW. Individual body components (head plus feet, hide, internal organs plus blood, and carcass) were weighed, ground, mixed, and subsampled for chemical analyses. Initial body composition was determined using equations developed from the composition of the baseline kids. The calculated daily maintenance requirement for NE was 77.3 +/- 1.05 kcal/kg(0.75) of empty BW (EBW) or 67.4 +/- 1.04 kcal/kg(0.75) of shrunk BW. The daily ME requirement for maintenance (118.1 kcal/kg(0.75) of EBW or 103.0 kcal/kg(0.75) of shrunk BW) was calculated by iteration, assuming that the heat produced was equal to the ME intake at maintenance. The partial efficiency of use of ME for NE below maintenance was 0.65. A value of 2.44 +/- 0.4 g of net protein/kg(0.75) of EBW for daily maintenance was determined. Net energy requirements for growth ranged from 2.55 to 3.0 Mcal/kg of EBW gain at 20 and 35 kg of BW, and net protein requirements for growth ranged from 178.8 to 185.2 g/kg of EBW gain. These results suggest that NE and net protein requirements for growing meat goats exceed the requirements previously published for dairy goats. Moreover, results from this study suggest that the N requirement for maintenance for growing goats is greater than the established recommendations.     

Effects of supplemental protein type on productivity of primiparous beef cows

Effects of supplemental degradable (DIP) and undegradable (UIP) intake protein on forage intake, BW change, body condition score (BCS), postpartum interval to first estrus, conception rate, milk production and composition, serum metabolites and metabolic hormones, and calf gain were determined using 36 primiparous Gelbvieh x Angus rotationally crossed beef cows. On d 3 postpartum, cows (average initial BW = 495 +/- 10 kg and BCS = 5.5 +/- 0.1) were randomly assigned to one of three dietary supplements (12 cows/treatment). Date of parturition was evenly distributed across treatment (average span of calving date among treatments = 2.4 +/- 2.5 d). Individually fed (d 3 through 120 postpartum) dietary supplements were 0.82 kg of corn and 0.23 kg of soybean meal per day (DIP), the DIP + 0.12 kg of blood meal and 0.13 kg of corn gluten meal per day (DIP + UIP), and 0.82 kg of corn, 0.07 kg of blood meal, and 0.08 kg of corn gluten meal per day in an isonitrogenous replacement of soybean meal (UIP IsoN). Cows had ad libitum access to native grass hay (8.5% CP) and trace-mineralized salt. Total OM intake was greater (P = 0.06) for DIP + UIP than UIP IsoN cows. At 30 d postpartum, DIP + UIP cows produced more milk than UIP IsoN, with DIP being intermediate; however, at 60 d postpartum, DIP + UIP and DIP cows were not different, but both had greater milk production than UIP IsoN (treatment x day interaction; P = 0.08). A treatment x day interaction (P = 0.06) for BCS resulted from DIP + UIP cows having the greatest BCS at 60, 90, and 120 d d postpartum and DIP having greater BCS than UIP IsoN cows only on d 60 postpartum. Serum insulin concentrations were highest (treatment x day interaction; P = 0.09) for DIP + UIP cows at 30 d postpartum but did not differ among treatment thereafter. Serum insulin-like growth factor-binding protein (IGFBP)-2 (34 kDa) and -3 (40 and 44 kDa) were greatest (P < 0.0003) for DIP cows. Serum urea-N concentrations were greater (P < 0.01) in DIP + UIP cows than in either DIP or UIP IsoN cows. However, postpartum interval to first estrus, conception rate, and calf weaning weights were unaffected (P = 0.35, 0.42, and 0.64, respectively) by treatment. Although UIP in addition to or in replacement of DIP affected milk production and blood metabolites, the productivity of these primiparous beef cows was not altered. Thus, the type of supplemental protein does not seem to influence productivity of primiparous beef cows in production systems with conditions similar to our experimental conditions.     

Studies of the transition cow under a pasture-based milk production system: metabolic profiles

This study describes the effect of parity (multiparous versus primiparous) and body condition score (BCS) at calving (<3 or > or =3; scale 1-5) on variations of BCS, body weight (BW) and metabolic profiles in Holstein cows grazing on improved pastures. Forty-two cows were studied (21 multiparous and 21 primiparous) from 2 months before to 3 months after calving. BCS, BW and milk production were measured every 2 weeks. Blood samples were taken every 2 weeks to determine total protein, albumin, urea, non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), cholesterol, aspartate aminotransferase (AST), calcium, phosphorus and magnesium. Primiparous cows had lower BCS during the early postpartum (PP) period and produced less milk than multiparous. In primiparous cows NEFA concentrations were higher during the early postpartum period; BHB levels were similar in both categories during this period. Primiparous cows showed a more unbalanced metabolic profile than multiparous cows, reflecting that they are recovering from the loss of BCS after calving with less success.     

Effect of dietary energy on milk production and metabolic hormones in thin, primiparous beef heifers

Thirty-six primiparous heifers were used to determine the effect of dietary energy on postpartum interval, milk production, serum concentrations of insulin, insulin-like growth factor I (IGF-I), growth hormone, and cerebrospinal fluid (CSF) concentrations of neuropeptide-Y (NPY). Low-quality hay was fed during the last trimester of pregnancy to achieve suboptimal calving weight (370 +/- 5 kg) and condition score (4.0 +/- .1). After calving, cows were allotted to one of four dietary treatments that differed in metabolizable energy. Experimental diets were fed at 2.5% of shrunk body weight and formulated to provide 1.8 (low), 2.1 (maintenance), 2.4 (maintenance high), or 2.7 (high) Mcal of ME/kg DM. Daily milk production was estimated at approximately 30, 60, and 90 d postpartum. Condition score change and weight change were defined as change from calving to d 90 postpartum. As energy intake increased, condition score change (P < .001), IGF-I (P < .001) and insulin (P < .01) increased and postpartum interval decreased (P = .04). No relationship existed between postpartum interval and CSF concentration of NPY (P > .1). Condition score change was positively associated with IGF-I and insulin (r = .71, P < .001; r = .38, P = .02, respectively) and negatively associated with GH (r = -.67, P < .001). Weight change and serum concentrations of GH did not differ (P > .10) among treatments. Increasing dietary energy intake was associated with a curvilinear increase in milk yield (P = .04) and percentage milk fat (P = .03) and a linear increase (P = .04) in energy available for milk production. Greater milk yield at d 30 was associated with a longer postpartum interval (r = .34, P < .05). In conclusion, a greater proportion of net energy is partitioned to maternal tissue realimentation when cows receive high compared to low-, maintenance-, or moderate-energy diets.     

Body condition at parturition and postpartum weight changes do not influence the incidence of short-lived corpora lutea in postpartum beef cows

Seventy-seven multiparous beef cows (Hereford and Angus x Hereford) with thin to moderate BCS at calving were used to evaluate the effects of body condition at parturition and BW change after calving on duration and occurence of luteal activity before and after first estrus. Blood samples were collected twice weekly after parturition to determine the occurrence of the first postpartum luteal activity (LA, progesterone > or = 0.5 ng/mL). Weight changes and BCS were determined at 2-wk intervals. Cows were exposed to bulls and observed twice daily for behavioral estrus. Luteal activity was classified as normal if plasma concentrations of progesterone were > or = 0.5 ng/mL for at least 11 d, or short if concentrations of progesterone were > or = 0.5 ng/mL for 10 d or less. The interval from parturition to first normal LA was shorter (P < 0.001) for moderate condition (BCS > or = 4.5) than for thin (BCS < or = 4) cows (58.3 +/- 3.2 vs. 93.3 +/- 5.1 d, respectively). Interval to first estrus also was shorter (P < 0.001) for moderate than for thin cows (53.3 +/- 3.7 vs. 89.3 +/- 5.6 d, respectively). Before the first normal LA, 78% of cows had an increase in progesterone for < 11 d. Postpartum weight change and BCS at calving did not influence the incidence of estrus associated with first normal LA. After the first estrus, 72% of cows had normal LA, 16% had a short luteal phase, and 12% lacked LA. Postpartum weight change and BCS did not influence the length of LA associated with the first estrus. Cows with normal LA had increased (P < 0.05) maximal concentrations of progesterone compared with cows that had a short luteal phase. When a transient increase in progesterone occurred before first behavioral estrus, 81% of cows had normal luteal function after estrus. We conclude that when beef cows are in thin to moderate body condition at calving, postpartum BW change and BCS at calving do not influence the duration of luteal activity before or after the first postpartum estrus.     

Relationships between body weight and milk yield during the early postpartum period and bull and technician and the reproductive performance of high producing dairy cows

The aim of this study was to evaluate the effect of body weight (BW) change during the early postpartum period and BW on day 50 post partum on the subsequent expression of estrus and fertility at first insemination before day 90 post partum. The data were derived from 1036 postpartum cows reaching 90 days in milk. The following data were recorded for each animal: lactation number, daily milk production at day 50 post partum, calving date, days in milk at estrus and at AI, insemination date, insemination number, inseminating bull, AI technician and body weight at calving, at day 50 post partum and at AI. Of the 1036 cows registered, 817 (78.9%) showed first estrus before day 90 post partum and were inseminated. Using logistic regression procedures and based on the odds ratio a one unit (kg) increase in the daily milk production at day 50 post partum and a one unit (kg) decrease in the BW between calving and day 50 post partum were related to a 1.03-fold increase and a 0.97-fold decrease in the estrus expression rate before day 90 post partum, respectively. Of the 817 cows inseminated before day 90 post partum, 437 became pregnant (53.5%). A one unit increase in the BW at day 50 post partum produced a 1.003-fold increase in the early fertility rate. Pregnancy rate before day 90 was also influenced by the season at calving, bull providing semen and technician. In conclusion, the register of BW during the postpartum period may be a useful tool for evaluating the nutritional status and its relationship with the subsequent reproductive efficiency in dairy cows.     

Energy balance in grazing Jersey cows in early lactation supplemented with peanut and sunflower oils

In this study, we evaluated the effects of supplementation with peanut and sunflower oils on intake and digestibility, milk yield and composition, energy balance (EB), changes in weight and body condition score (BW and BCS), and blood metabolites of Jersey cows on pasture in early lactation. Twenty-four cows were distributed in a randomized block design where they received the following treatments: concentrate without oil (CON), concentrate plus 59.6 g/kg DM peanut oil (PEA), concentrate plus 59.6 g/kg DM sunflower oil (SUN), and concentrate plus 59.6 g/kg DM of a 1:1 mixture of peanut oil and sunflower oil (MIX). The data were analyzed at 30 and 60 days in milk (DIM). Oil supplementation did not affect total dry matter intake or forage intake. The treatment SUN reduced daily milk yield, 4% fat-corrected milk yield, and milk fat, while the other treatments generated similar results. The treatment SUN reduced the milk net energy and the use efficiency of the NE_L for milk production and BW and BCS changes, and improved EB up to 60 DIM. On tropical pastures, supplementation with unsaturated oils for cows in early lactation does not result in better milk performance. The supplementation with sunflower oil improves the energy balance in early lactation.     

Effects of supplementation with high linoleic or oleic cracked safflower seeds on postpartum reproduction and calf performance of primiparous beef heifers

Primiparous Angus x Gelbvieh (n = 36) rotationally crossed beef cows (initial BW = 487.9 +/- 10.5 kg, body condition score = 5.5 +/- 0.02) were utilized to determine effects of supplemental safflower seeds high in linoleic (76% 18:2) or oleic (72% 18:1) acid on cow BW change, body condition score, milk production and composition, calf weight gain, cow serum metabolites, and metabolic hormones. On d 3 postpartum, cows were randomly assigned to one of three isonitrogenous dietary supplements with equal total quantity of TDN: corn-soybean control supplement (n = 12); high-linoleate safflower seeds (n = 12); or high-oleate safflower seeds (n = 12). Safflower-seed supplements were formulated to provide 5% DMI as fat. Supplements were individually fed from d 3 postpartum through 90 d postpartum. Cows had ad libitum access to native grass hay (7.8% CP), trace-mineralized salt, and water. Date of parturition was evenly distributed across treatments with all cows calving within 14 +/- 0.8 d. There were no differences (P = 0.65) in total OM intake among treatments. Although cow BW change did not differ (P = 0.33) by treatment, supplementation influenced cow body condition score (P = 0.02) with linoleate-supple-mented cows in higher (P = 0.005) condition overall than oleate-supplemented cows (5.1 +/- 0.06 vs 4.9 +/- 0.06). Twenty-four-hour milk production did not differ (P = 0.68) among treatments. Percentage milk fat was not different at d 30; however, at d 60 and d 90 percentage milk fat was greater (P ( 0.05) in control and oleate-supplemented cows than in linoleate-supplemented cows. Calf BW gains (P = 0.27) and adjusted 205-d weights (P = 0.48) were not affected by supplement treatment. Supplementation did not influence serum concentrations of glucose (P = 0.38), NEFA (P = 0.61), GH (P = 0.29), IGF-I (P = 0.81), insulin (P = 0.26), or IGF-I binding proteins (P > or = 0.11). Days to conception did not differ (P = 0.40) among treatments. Although overall productivity of the primiparous cows and their calves was not altered by safflower-seed supplementation, differential effects were noted between supplements. Oleate supplementation increased percentage milk fat at d 60, and cow body condition score was lower than in linoleate-supplemented cows. Linoleate-supplemented cows had greater body condition scores by 90 d postpartum than either corn-soybean- or oleatesupplemented cows.     

Effects of energy and lasalocid on productivity of first-calf heifers

One hundred forty-three crossbred, fall-calving first-calf heifers were used to determine the effects of two levels of energy and two levels of lasalocid on cow-calf productivity. Diets fed for approximately 110 d prepartum were calculated to provide a daily intake of 15.3 (LE) or 18.0 (HE) Mcal ME; diets fed for approximately 130 d postpartum were calculated to provide a daily intake of 17.8 (LE) or 21.0 (HE) Mcal ME. Two supplements were fed with each energy level to provide a calculated 0 (C) or 200 mg.hd-1.d-1 lasalocid (L). Heifers fed HE gained .06 kg more (P = .08) per day prepartum than LE heifers. There was an interaction (P less than .05) between treatment and prepartum days on trial for heifer weight approximately 2 wk prepartum and body condition at calving. Energy had no effect on heifer weight at 2 wk prepartum or condition score at calving when estimated and compared at 90 d on trial. However, regression estimates for 130 d on trial showed that HE heifers would have been 19 kg heavier (P less than .001) and would have had .4 unit higher condition score (P less than .01) than LE heifers. Energy and lasalocid had no effect (P greater than .05) on hip height or pelvic area at calving or on calf birth weight, calving ease score or gestation length. Cows fed HE weighed 17 kg more (P less than .05) and had .5 unit higher (P less than .001) condition score than LE cows at approximately 130 d postpartum. Lasalocid had little effect on postpartum changes in weight or body condition. Lasalocid supplementation to the LE diet tended to increase milk production and calf weight, whereas supplementation to the HE diet did not. Feeding the LE diet decreased (P less than .05) cycling activity by 18 percentage points and decreased (P less than .01) overall pregnancy rate by 25 percentage points. Lasalocid had no influence on reproductive performance.     

Response to metabolic challenges in early lactation dairy cows during treatment with bovine somatotropin

Milk production is increased in lactating cows treated with bovine somatotropin (bST) because a greater portion of absorbed nutrients are partitioned for milk synthesis. This homeorhetic action may be caused by alterations in response of key tissues to homeostatic signals. To examine this theory, acute metabolic challenges were administered to 8 multiparous Holstein cows (61 +/- 2 days postpartum) receiving daily subcutaneous injections of pituitary-derived bST (26.3 mg) or excipient during two 14-day treatment periods (crossover experimental design). Treatment with bST increased milk yield 12%. Feed intake did not change so that net energy balance decreased (+ .5 vs. -4.3 Mcal/day). Plasma concentrations of nonesterified fatty acids (NEFA) were chronically elevated in bST-treated cows, consistent with energy balance differences. However, baseline concentrations of glucose, insulin, and glucagon in plasma did not differ. On the last 3 days of treatment, individual metabolic challenges were administered via jugular cannulas: epinephrine (700 ng/kg BW), glucose (250 mg/kg BW), insulin (1.0 micrograms/kg BW), and glucagon (175 ng/kg BW). Plasma glucose was reduced after the insulin challenge to a lesser extent during bST treatment. In bST-treated cows, the increase in plasma NEFA in response to epinephrine was greater, and NEFA concentrations were lowered to a greater extent after insulin and glucose challenges. Glucose, insulin, and glucagon removal rates were not altered, nor was plasma glucose response to epinephrine or glucagon challenges. Treatment of lactating cows with bST primarily altered the response of adipose tissue to homeostatic signals which affect lipid metabolism.     

Energy and protein requirements for growth and maintenance of F1 Nellore x Red Angus bulls, steers, and heifers

A comparative slaughter trial was conducted with 36 F1 Nellore x Red Angus calves (12 steers, 12 bulls, and 12 heifers), averaging 274 kg of BW, to assess the net requirements of protein and energy for growth and maintenance. Three cattle from each group (i.e., steers, bulls, and heifers) were slaughtered at the beginning of the trial to determine the initial body composition. The remaining calves were randomly assigned to 1 of 3 treatments: maintenance (diet containing 70% of DM as corn silage fed at 1.2% of BW daily) or concentrate at 0.75 or 1.5% of BW daily with corn silage available for ad libitum consumption. The diets were isonitrogenous (2% N, DM basis). The experimental design provided ranges in ME intake, BW, and ADG for the development of regression equations to predict the maintenance requirements for NE and net protein (MRNE and MRNP, respectively) and the growth requirement for NE and net protein (GRNE and GRNP, respectively). After 84 d of growth, the cattle were slaughtered. The cleaned gastrointestinal tracts, organs, carcasses, heads, hides, tails, feet, blood, and tissues were weighed to measure empty BW (EBW). These parts were ground separately and subsampled for chemical analyses. For each animal within a period, DMI was measured daily and samples of feces were collected to determine diet digestibility. There were no differences in MRNE (P = 0.06) among groups. The combined data indicated a MRNE of 71.2 kcal x kg(-0.75) of EBW x d(-1), with a partial efficiency of use of ME to NE(m) of 0.71. The partial efficiency of use of ME to NE for growth was 0.54 for bulls, 0.47 for steers, and 0.54 for heifers. The GRNE for steers and heifers were similar (P = 0.15) but were 18.7% greater (P = 0.03) for steers and heifers than for bulls. The MRNP did not differ among groups and averaged 2.53 g of CP x kg(-0.75) of EBW x d(-1). Likewise, GRNP was not different among groups. The percentage of retained energy deposited as protein (RE(p)) increased as the content of retained energy in the gain (RE(c), Mcal/kg of empty body gain) decreased. The RE(p) equation of the pooled data was 46.5 x e(-0.2463 x RE(c)). We conclude that the energy requirement of crossbred Bos indicus x Bos taurus for maintenance might be less than that of purebred Bos taurus and that RE(p) is nonlinearly, negatively correlated with RE(c). The GRNE was less for bulls than for steers and heifers. However, we found no differences in MRNE, MRNP, and GRNP for bulls, steers, and heifers of Nellore x Red Angus crossbreds.