Annotations file for RDA184Page: 1Author/editor: is short title acceptable?Reproductive and Endocrine Changes in Dairy Cows Given GnRH at Different Intervals Postpartum

Contents
The reproductive organs of 91 cows in the university herd were palpated at least twice per week from 12 to 53 days postpartum (PP). Based upon uterine and cervical involution and tone, ovarian condition and fluid discharge at 12 to 18 days PP they were classified as normal or abnormal. Within each group they were randomly assigned to receive either saline or 100 μg of GnRH at 12 to 18 days or 100 μg of GnRH at 22 to 28 days PP. Milk samples were taken for progesterone determinations three times per week until the first breeding or up to 90 days PP. A subset of 23 cows completed a frequent blood sampling programme at 0 h (just prior to treatment), 1, 2, 4, 8 and 12 h later and every 12 h for 15 days following treatment. Values for milk and serum progesterone in samples taken during the same time period were highly correlated, r = 0.90, and were consistent with ovarian changes detected by palpation. Cows classified as normal initially continued to be normal, and GnRH had little effect. In the abnormal groups of cows at 28 days PP, 41% of the saline group and 77% of those treated with GnRH at 12 to 18 days PP had fully involuted uteri. Early treatment of abnormal cows with GnRH improved the reproductive efficiency, resulting in 95 days open compared with 129 days for saline-treated abnormals. In conclusion, treatment with GnRH was effective in hastening the return to normal of cows classified initially as abnormal, and appears to be cost effective in maintaining an optimal calving interval.     

Reproductive performance in dairy cows following postpartum treatment with gonadotrophin releasing hormone and/or prostaglandin: a field trial.

Three hundred and five Holstein Friesian cows were given either 250 micrograms gonadotrophin releasing hormone (GnRH) or saline on day 15 postpartum followed by 500 micrograms cloprostenol or saline on day 24 postpartum. Four treatment groups were formed using random allocation: Group I -- placebo (Day 15)/placebo (Day 24), Group II -- GnRH (Day 15)/placebo (Day 24), Group III -- placebo (Day 15)/cloprostenol (Day 24), Group IV -- GnRH (Day 15)/cloprostenol (Day 24). Double blind techniques were used during the follow-up period. Rectal palpation, to assess uterine involution and ovarian activity was performed just prior to each treatment and again at 28 days postpartum. In addition blood samples were collected at 15, 24 and 28 days postpartum for measurement of plasma progesterone. There were no significant differences among treatment groups with respect to services per conception, number of heats detected before first service and culling for infertility. Cows treated only with GnRH had an increased calving to first estrus and calving to first breeding interval, and tended to have an increased calving to conception interval. Treatment with cloprostenol significantly decreased calving to conception and calving to first observed estrus intervals. Treatment with GnRH on day 15 postpartum resulted in a significant increase in the subsequent incidence of pyometra and prebreeding anestrus. On the other hand, cloprostenol treatment on day 24 postpartum resulted in a decreased incidence of pyometra, regardless of GnRH treatment and a decreased incidence of prebreeding anestrus in GnRH treated cows compared to cows receiving only GnRH at day 15 postpartum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of gonadotrophin releasing hormone on reproductive performance of dairy cows with retained placenta.

The effects of gonadotrophin releasing hormone (GnRH) on the reproductive performance of dairy cows with retained placenta were studied. Three hundred and seventy-eight cows diagnosed as having retained placenta received intramuscular injections of either 2 mL sterile water or 200 micrograms of GnRH in 2 mL sterile water between day 8 and day 14 postpartum. Rectal palpation was performed at the time of treatment and ten to 20 days after treatment in order to determine the rate of uterine involution. Thereafter, monthly rectal examinations were carried out until insemination. Pregnancy diagnosis was made by rectal palpation at 40 days or more after breeding. Using the entire experimental population, there were no significant differences between GnRH-treated and control cows for the rate of uterine involution, the occurrence of reproductive problems, the interval from parturition to first observed estrus, the interval from parturition to first insemination, the interval from parturition to conception, the number of services per conception, the total number of services per cow regardless of conception and the incidence of culling for infertility. When the data for herds in which breeding began earlier in the postpartum period (herds having a mean less than or equal to 80 days from parturition to first service for retained placenta cows) were considered, the GnRH treatment resulted in a significantly shorter (p less than or equal to 0.01) calving to conception interval as compared to control cows. Also, there was a significant reduction (p less than or equal to 0.05) in the total number of services per cow regardless of conception and a significant reduction in the interval from parturition to first service.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reproductive performance of Holstein cows administered GnRH analog HOE 766 (Buserelin) 26 to 34 days postpartum

During the fourth week postpartum, 443 healthy Holstein cows milked thrice daily were randomly divided among four groups to receive 0, 2, 8 and 32 micrograms of the GnRH analog HOE 766. Intervals from calving to first estrus and to first breeding, from breeding to conception and conception rates at first breeding were calculated to measure treatment response, and progesterone was measured in the fat-free portion of milk samples collected twice weekly during the first 4 wk following treatment. Uterine involution at the time of treatment was estimated by palpation per rectum. Twenty percent of the cows examined were classified as having delayed uterine involution (abnormal). By analyzing milk progesterone patterns it was determined that 38% of the animals were in the luteal phase of an estrous cycle when treated. Cows without luteal tissue (less than 1 ng of progesterone/ml milk) given 8 or 32 micrograms of HOE 766 increased in progesterone to greater than or equal to 1 ng/ml within 7 d in 77 and 72% of the cows compared with 40 and 57% for cows receiving 0 and 2 micrograms (P less than .05). This increase in progesterone was followed by a normal estrous cycle within 4 wk in a higher proportion of cows treated with the two higher doses of GnRH analog (87 and 86%) compared with 67 and 70% of those receiving 0 or 2 micrograms of the analog (P less than .005). There were no treatment differences (P greater than .05) for other traits analyzed, but cows with a normal progesterone cycle were observed in estrus and were bred sooner (P less than .01) than those with irregular progesterone patterns. It was concluded that the GnRH analog hastened the onset of normal ovarian cycles in cows milked thrice daily.     

Interrelationships between ambient temperature, age at calving, postpartum reproductive events and reproductive performance in dairy cows: a path analysis.

Path analysis was used to determine the interrelationships between ambient temperature, age at calving, postpartum reproductive events and reproductive performance in dairy cows. The data used in the analysis were collected on 226 Holstein-Friesian cows calving in a commercial dairy herd during a 17 month period (May 1, 1981 to October 1, 1982). The data were obtained from a double blind study evaluating the effects of gonadotrophin releasing hormone and cloprostenol in postpartum cows. Rectal palpation to assess uterine involution and ovarian activity was performed on each cow on days 15, 24 and 28 postpartum. At the same time, blood samples were collected for subsequent progesterone assay. Data were recorded on the occurrence of reproductive diseases and events from the time of parturition until the diagnosis of pregnancy or until the cow left the herd in the case of culled cows. There was an increase in the incidence of retained placenta, in the percentage of cows with abnormal vaginal discharge in the early postpartum period as well as a delay in uterine involution during the winter months. In addition, cows calving during the winter had prolonged intervals to first estrus, first service and conception compared to cows calving during the summer. (Cows calving during the warmest months, on average, were seen in estrus 24 days sooner, received first service 42 days sooner and conceived 27 days sooner than cows calving during the coldest months of the year).(ABSTRACT TRUNCATED AT 250 WORDS)     

Different Types of Postpartum Luteal Activity Affected by the Exposure of Heat Stress and Subsequent Reproductive Performance in Holstein Lactating Cows

The aim of the present study was to determine the effect of heat stress on postpartum (PP) luteal activity and subsequent reproductive performance in lactating cows. Thirty Holstein–Friesian (HF, ≥75%) cows (hot season, n = 15 and cool season, n = 15) were studied over 60 days after calving. The changes of temperature‐humidity index (THI) were monitored within both seasons. Body condition scores (BCS), uterine involution and the ovarian structures were recorded. Plasma samples were obtained three times a week for the analysis of progesterone (P4) and prostaglandin F_2α metabolite (PG metabolite). Subsequent reproductive performance of the cows, calved within the same period was also evaluated. The means of THI for hot and cool seasons varied between 84–87 and 78–83 respectively. A drop of the mean BCS was recorded at 5 weeks PP in the cows during hot season (p < 0.01), however a delay of uterine involution during early PP period in hot season was not clearly seen. The cows with normal PP ovarian cyclicity during hot and cool seasons were 4/15 (26.7%) and 9/15 (60.0%) respectively. A higher percentage of abnormal luteal activity was found in the cows during hot season (p = 0.07) and delayed luteal cyclicity/anovulation was the most pronounced atypical P4 profile. The levels of PG metabolite were not different between groups and the relationship between the levels of PG metabolite and the time of uterine involution was not evident (p > 0.05). The heat detection rates and the pregnancy rates were higher in the cows during cool season (p < 0.05). Additionally, the higher first AI conception rates during cool season were recorded (p = 0.06). In conclusion, heat stress conditions had negative effects on BCS and altered a normal process of ovarian resumption PP, consequently resulted in lower reproductive performance in a tropical dairy herd.     

Postpartum reproductive performance in dairy cows. I: Influence of animal, breed and parity

The purpose of this study was to evaluate the influence of animal, breed and parity on postpartum reproductive functions in dairy cows. A total of 141 cows were included in the experiment, which was carried out as part of a study on traits affecting longevity in Swedish dairy cows. The cows belonged to 4 different breed-groups and were 1st to 5th calvers. The duration of the study was 3 years and 44 cows were followed during 1 postpartum period, 49 cows during 2 consecutive periods, 43 cows during 3 periods and 5 cows during 4 periods.The cows were clinically examined, by rectal palpation, at 10-day intervals between calving and first AI, which was at first normal oestrus more than 50 days after calving. External signs of heat were checker and recorded three times daily by the herdsmen. Blood samples for progesterone assay were taken at days 10, 15 and 20 after calving and thereafter every 10th day until first AI. Samples taken at days 10, 15 and 20 were also assayed for content of 15-keto-13,14-dihydro-PGF_2α.Heat detection records, records from clinical examinations and plasma progesterone assays were chronologically compiled for each postpartum period and based on this, intervals between calving and postpartum ovulations, recorded uterine involution, 1st and subsequent oestrus and regular reproductive functions were estimated. Least-squares methods were used for the statistical evaluation of data.The results indicate a large variation within and between cows in postpartum reproductive performance. In the total material 1st ovulation occurred before recorded uterine involution and there was a close relationship between 1st ovulatory oestrus and the onset of regular reproductive functions. The interval between calving and 1st ovulation significantly influenced the length of the first cycle in the sense that a large proportion of the early ovulating cows had a short interval between 1st and 2nd postpartum ovulations. The large variations were also evident in the plasma levels of 15-keto-13,14-dihydro-PGF_2α. There was a marked decline between days 10 and 15 postpartum and most cows were close to basal levels at 20 days postpartum.The individual cow had a significant influence on intervals from calving to recorded uterine involution, 1st ovulatory oestrus, regular reproductive functions and conception. The breed influence was significant for intervals between calving and 1st ovulation and recorded uterine involution whereas the parity of the cow only influenced the interval between calving and recorded uterine involution.     

Effect of dystocia on subsequent reproductive performance and functional longevity in Holstein cows

The objective of this study was to evaluate the effect of dystocia on the reproductive performance and functional longevity in Iranian Holsteins. Data consisted of 1 467 064 lactation records of 581 421 Holstein cows from 3083 herds which were collected by the Animal Breeding Center of Iran from April 1987 to February 2014. Reproduction traits in this study included interval from first to second calving, days open and days from first calving to first service. The generalized linear model was used for the statistical analysis of reproductive traits. Survival analysis was performed using the Weibull proportional hazards models to analyse the impact of dystocia on functional longevity. The incidence of dystocia had an adverse effect on the reproductive performance of dairy cows. Therefore, reproductive traits deteriorated along with increase in dystocia score (p < 0.05). The culling risk was increased along with increase in the score of dystocia (p < 0.0001). The greatest culling risk was observed in primiparous cows, small herds and low‐yielding cows (p < 0.0001). Also, the lowest culling risk was found for cows calving at the youngest age (<27 months), and cows with age at first calving >33 months had the greatest risk (p < 0.0001). The results of current study indicated that dystocia had important negative effects on the reproductive performance and functional longevity in dairy cows, and it should be avoided as much as possible to provide a good perspective in the scope of economic and animal welfare issues in dairy herds.     

Failure of an intramuscular injection of an analogue of gonadotrophin-releasing hormone 11 to 13 days after insemination to increase pregnancy rates in dairy cattle

At 11 to 13 d after insemination, 1028 dairy cows on 19 farms were given an intramuscular injection of 10 micrograms of the GnRH analogue buserelin. Their reproductive performance was compared to 1022 control cows receiving a placebo. The GnRH analogue-treated cows had fewer short interoestrous intervals compared to the control cows, but there were no significant differences in pregnancy rates to either the insemination preceding or following treatment, in calving to conception interval, or to percent pregnant by the end of mating. There were no differences between treatments in herds of high, average or low pregnancy rate, in 2-year-old cows or cows greater than 2-years-old and in cows calved 40 d or less, or greater than 40 d. The use of 10 micrograms of the GnRH analogue, buserelin, 11 to 13 d after insemination, cannot be recommended as a method of improving reproductive performance in dairy herds.     

Postpartum reproductive function in Finnish Ayrshire and Friesian cows after three subsequent parturitions

The postpartum reproduction functions of 84 Finnish Ayrshire and Friesian cows were studied on an experimental farm. The cows were divided according to type of feed into 2 groups of equal size: a hay-urea group and a silage group. The duration of the study was 3 years. Eighty-four cows were followed during their first postpartum period, 63 during 2 and 57 during 3 consecutive post partum periods.The cows were examined clinically by rectal palpation, and milk samples for progesterone assay were taken 3 times a week between calving and first insemination. External signs of heat were checked 3 times a day by the herdsmen.Intervals from calving to completed uterine and cervical involution, appearance of first palpable follicle, onset of first luteal function and onset of regular ovarian function were recorded. Intervals from calving to the first observed heat and to pregnancy were measured and the rate of successful pregnancies at the first insemination was calculated.Least squares methods were used for evaluation of the effect of individual cow, breed, parity/year and type of feed on postpartum reproductive function.The cows in the herd seemed to have equal reproductive functions which were influenced by the conditions during each year/parity rather than by the breed or type of feed.Individual cow effect was significant for the rapidity of uterine involution. Breed had no significant effect on any of the parameters studied.The effect of type of feed alone was not significant for any parameter, but when studying the intervals from calving to uterine involution and initiation of luteal function differences between the feed groups were noted within parity/year.The percentage of cows showing heat before the first dioestrus (luteal phase) increased with parity/year, and the first dioestrus was shorter than the second. The percentage of cows showing postoestrous bleeding increased with number of oestrous cycles post partum.     

Effect of relationships among clinical mastitis incidence,reproductive performance,and culling rate on the lifetime of dairy cows at Hiroshima University Farm

Farm managers' decision to cull dairy cows is based on the cows' milk production, history of disorder(s), and reproductive performance, each of which affects dairy cows' lifetime (herd life and productive lifespan). We investigated the relationships among the incidence of clinical mastitis (CM), the reproductive performance, and the culling rate. We also assessed the effects of these relationships on the lifetimes of dairy cows, using the records made before and after the introduction of an automatic milking system (AMS) at Hiroshima University Farm. Milk yield, CM incidence density, and culling rate of dairy cows increased after the AMS introduction. The CM incidence was associated with an elongation of the calving interval in cows with the same parity. CM in the 1st parity might have caused the reductions of the cows' lifetime and their parity at culling. A higher age at first calving (AFC) was associated with an increase in culling rate but did not lead to a significant decrease in lifetime. Investigations of the factors mediating CM in the 1st parity or AFC with CM incidence or culling rate in the later stages might contribute to the control of lifetime of dairy cows.     

Interrelationships between postpartum events, hormonal therapy, reproductive abnormalities and reproductive performance in dairy cows: a path analysis.

Path analysis was used to determine the interrelationships between postpartum administration of gonadotrophin releasing hormone and cloprostenol and the occurrence of reproductive disease and reproductive performance in dairy cows. The data analysed were those collected on 226 Holstein-Friesian cows calving in a commercial dairy herd during a 17 month period (May 1, 1981 to October 1, 1982). Cows administered gonadotrophin releasing hormone at day 15 postpartum experienced an improved rate of uterine involution as determined by rectal palpation nine days later. Although this improved rate of uterine involution reduced the risk of pyometritis, it actually directly delayed conception. Also, gonadotrophin releasing hormone therapy directly resulted in an increased incidence of pyometritis which in turn resulted in an increase incidence of cystic ovarian disease and anestrus. The occurrence of these abnormalities resulted in increased intervals from calving to first observed estrus, first service and conception. In addition to this effect, the administration of gonadotrophin releasing hormone was also associated with increased plasma progesterone concentrations at days 24 and 28 postpartum which delayed conception. Cloprostenol therapy at day 24 postpartum resulted in a decreased plasma progesterone concentration at day 28 postpartum which was directly and indirectly associated with a decrease in the calving to conception interval. The indirect effects were mediated by a reduction in days to first estrus. Cloprostenol therapy also directly resulted in a decreased calving to first observed estrus interval for reasons not attributable to the level of progesterone at day 28.     

Effects of lasalocid on circulating concentrations of leptin and insulin-like growth factor-I and reproductive performance of postpartum Brahman cows

Objectives were to determine effects of lasalocid on reproductive performance and serum concentrations of leptin and IGF-I, and to correlate concentrations of leptin and IGF-I with reproductive performance of beef cows. Forty-one purebred, multiparous Brahman cows were blocked to control (C; n = 20) or lasalocid (L; n = 21) treatments by BW, BCS, and predicted calving date. Treatment began 21 d before expected calving. Cows were each fed 1.4 kg daily of an 11:1 corn:soybean meal supplement, with the L group receiving 200 mg of lasalocid/cow daily. Cows and calves were weighed, and cow BCS was assessed at calving and at 28-d intervals thereafter. Blood samples were collected weekly precalving, at parturition, and twice weekly thereafter. Sterile marker bulls were maintained with cows for estrous detection. Six days after estrus, ovaries were evaluated for corpus luteum formation, and blood samples from d 6, 7, and 8 after estrus were collected. Serum samples were assayed for progesterone (P4), IGF-I, and leptin concentration. Progesterone concentrations > 1 ng/mL were considered indicative of a functional corpus luteum. Treatment ended after completion of a normal estrous cycle, and cows removed from treatment were placed with a fertile bull equipped with a chinball marker. There were no treatment differences in calving date, calf sex, cow BW, BCS, calf BW, calf ADG, or in serum concentrations of P4, IGF-I, or leptin. Prepartum cow ADG was increased (P < 0.01) in L cows and tended (P < 0.011) to be increased from calving to d 56 after calving in L cows. Postpartum interval (PPI) was not affected by treatment; however, a greater percentage (P < 0.05) of L cows conceived by 90 d after calving (43% L vs. 15% C). First-service conception rate tended (P < 0.08) to be greater in L vs. C cows (68 vs. 40%), but pregnancy rate was not different (P < 0.12; 86% for L vs. 65% for C). There were no treatment differences (P > 0.18) for serum IGF-I concentrations. At calving, leptin was positively correlated with IGF-I (P < 0.04; r = 0.32), BCS (P < 0.06; r = 0.29), and cow BW (P < 0.02; r = 0.36), and was negatively correlated with PPI (P < 0.06; r = -0.29). These results provide evidence that feeding an ionophore before calving and during the postpartum period may increase the number of cows that rebreed to maintain a yearly calving interval. Cows with higher concentrations of leptin postpartum may exhibit shorter PPI.     

Risk factors and the economic impact of ovarian cysts on reproductive performance of dairy cows in Korea

The objectives of this study were to determine the risk factors for development of postpartum ovarian cysts by evaluating several reproductive factors in individual cows, and to determine the economic impact of ovarian cysts on subsequent reproductive performance in dairy herds in Korea. The data, including cow parity, abnormal puerperium, endometritis, body condition score (BCS), and breeding status were collected from 634 cows in 9 dairy herds. We used logistic regression to evaluate the effects of these factors on ovarian cysts. A stepwise procedure, used to obtain the appropriate model with alpha=0.05, revealed that cow parity was the most important risk factor for ovarian cyst development within 8 weeks postpartum, while development of endometritis and BCS loss>or=1 from the dry period to 8 weeks postpartum were the most important risk factors for ovarian cyst development beyond 8 weeks postpartum. The occurrence of ovarian cysts beyond 8 weeks postpartum prolonged (P<0.01) the mean intervals from calving to first service (27 days) and conception (77 days), and increased (P<0.05) the culling rate (7.8%), while ovarian cyst development within 8 weeks postpartum did not affect (P>0.05) the mean intervals from calving to first service and conception or the culling rate. The economic loss resulting from the occurrence of ovarian cysts was estimated at approximately 823,996 won ($687) due to effects on the cost of nutrition, average growth of calves, labor and medical costs, and culling. These results suggest that cow parity is correlated with the development of ovarian cysts within 8 weeks postpartum, and endometritis and BCS loss>or=1 from the dry period to 8 weeks postpartum are correlated with the development of ovarian cysts after 8 weeks postpartum, which decreases reproductive performance and results in economic loss in dairy herds in Korea.     

Hormonal, estrual, ovulatory and milk traits in postpartum dairy cows following multiple daily injections of oxytocin

Release of oxytocin at suckling or milking may delay onset of estrous cycles in postpartum cows. Twenty lactating Holsteins of mixed parity were given 100 mU oxytocin iv (n = 10) or 2 ml saline (control; n = 10) via jugular catheters at 0530, 0930, 1730 and 2130 daily from calving (d o) until 28 d postpartum. All cows were milked twice daily at 0130 and 1330. Blood was collected thrice weekly (Monday, Wednesday, Friday at 0530) for 12 wk and analyzed by radioimmunoassay for progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum. On d 12, blood was collected every 15 min for 6 h via jugular catheters and concentrations of luteinizing hormone (LH), cortisol and PGFM were determined. Rate of involution of the reproductive tract was estimated twice weekly by palpation per rectum. Overall mean, baseline concentrations, number of pulses/6 h, and pulse duration of LH on d 12 were similar among treatment groups. However, oxytocin seemed to reduce (P less than .10) pulse amplitude of LH in multiparous cows (.4 +/- .2 vs .8 +/- .1 ng/ml), but not in primiparous cows. Concentrations of cortisol and PGFM in serum on d 12 were unaffected by treatment. The average intervals from calving to first ovulation, based on changes of progesterone in serum and the intervals to first estrus, were similar between treatment groups. Rates of involution of the cervix and uterus also were similar between treatments. Milk yield, percent protein in milk and somatic cell counts did not differ between treatment groups. However, percent fat in milk tended to be higher (P less than .10) in cows given oxytocin than in controls (3.99 +/- .22 vs 3.68 +/- .21). These data indicate that multiple daily injections of oxytocin did not affect: 1) length of anestrus and anovulation in postpartum dairy cows, 2) LH release and 3) rates of cervical and uterine involution.     

Relative calving date of first-calf heifers as related to production efficiency and subsequent reproductive performance

Relative date of first calving of beef heifers was studied in relation to production efficiency and subsequent reproductive performance. Crossbred heifers were managed in a drylot environment for 1 yr with feed intake measured through weaning of the first calf. Mean heifer age at entry into drylot was 572 d. Production traits were evaluated by calving group (CG), where CG1 included records of heifers calving (and calves born) in the first 21 d of the calving season for a particular year, CG2 included those calving from 22 through 42 d and CG3 included those calving after 42 d. Calving groups did not differ significantly for preweaning calf ADG, but weaning age differences resulted in heavier weaning weights for CG1 compared with CG2 and CG3. An earlier relative calving date was associated with increased cumulative feed energy intake of heifers and their calves during the 1-yr test period. In terms of production efficiency, the weaning weight advantage of earlier calving was offset only partly by the increased feed energy intake of the dam-calf unit, resulting in 6.3 Mcal (12.4%) less ME per kg calf weaning weight for CG1 vs CG3 for the 1-yr period. Within a limited calving season, earlier calving dams tended to be biologically and economically more efficient because a greater proportion of their annual production cycle was in a productive (lactating) mode, diluting maintenance costs as a fraction of all costs. Heifers in CG1 also tended to calve earlier than CG3 heifers for the second calf. Calving interval was a biased measure under the management conditions of a limited breeding season and culling of open cows.     

Effects of body composition, pre- and postpartum energy level and early weaning on reproductive performance of beef cows and preweaning calf gain

Mature Charolais x Angus rotational cross cows were adjusted to moderate body condition by d 190 of gestation then randomly blocked to a maintenance (ME) or low-energy (LE) diet. At parturition, the 128 cows were randomly allotted within prepartum (PRP) diet to a high-energy (HE) or LE diet. At d 30 postpartum (PP), cows were randomly blocked to two treatments in which calves were weaned early (EW) or normally (NW) at 7 mo of age. Cows receiving a LE PRP diet had lighter calves at birth (34.7 vs 39.0 kg) and 105 d (127.9 vs 144.6 kg). Prepartum and PP energy interacted to affect postpartum anestrous interval (PPI, d) and cycling activity (%), respectively (LE-LE = 72.6, 33.3; LE-HE = 54.3, 56.3; ME-LE = 65.7, 52.9; ME-HE = 68.4, 54.3). High PP energy averaged over PRP diet increased (P less than .10) pregnancy rate by 22.7% and 105-d calf weight by 15.1 kg. Early weaning reduced PPI by 24.3 d (P less than .01) and first service conception rate by 21.7% (P less than .10). Cycling activity within 60 d PP was affected (P less than .01) by PRP diet and suckling status (LE-EW = 62.5, LE-NW = 26.7, ME-EW = 88.9, ME-NW = 13.3%). Thin cows had a longer PPI but had a higher first service conception rate than moderate and fleshy cows. Higher pregnancy rates were observed in cows approaching or maintaining average body condition from parturition to conception than for cows moving away from moderate body condition. Results suggest that fleshy and thin cows at parturition should be managed to approach moderate body condition before the breeding season to optimize reproductive performance and preweaning calf gain.     

Simulated selection for reproductive rate in beef cattle

Computer simulation was used to evaluate four selection strategies for reproductive success in beef cattle. The strategies were no culling; culling of nonpregnant heifers; culling of nonpregnant heifers and cows nonpregnant twice; culling all nonpregnant females. In addition, simulations were conducted utilizing method four for 20 yr, then changed to method three for an additional 20 yr. Cows were removed from the herd at age 10 if not previously culled. Because reproduction is a threshold character, an underlying normally distributed liability that influences whether or not a cow will produce a calf was assumed with a heritability estimate of .2, a mean of zero and a standard deviation of one. Regressions of breeding value for reproduction and calving rate on year of selection were calculated assuming initial calving rates of 80 and 90%. Linear and quadratic effects for breeding value were present for all selection methods at both initial rates. All primary breeding value regressions were different than that for no culling. At the 90% initial calving rate, methods three and four were different from method two. There were no differences among any regressions for calving rate. Progress for breeding value was more regular than for calving rate; maximum progress for breeding value in 40 yr was approximately .32 standard deviations for selection method four. Calving rate was more erratic, although calving rate increased approximately 7% as a result of 40 yr of selection using method four at the 80% initial calving rate. It appears that much of the improvement attained by any method of selection occurred in the first 20 yr.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effects of heat stress during pregnancy on postpartum reproductive changes in Holstein cows

Effects of heat stress during the last third of gestation on reproductive changes postpartum were studied in Holstein cows. Cows and heifers 160 to 190 d of gestation were assigned in June 1978 to shade (n = seven cows and two heifers) or no shade (n = eight cows and two heifers) management treatments. After parturition, all cows (n = 19) were moved to the milking herd and managed uniformly. On the day of calving and on each Monday, Wednesday and Friday thereafter until d 50 postpartum, jugular blood samples were collected. Beginning approximately 7 d postpartum, the reproductive tract of each cow was examined rectally after collection of blood samples. Estrus was monitored twice daily and cows were inseminated after d 45 postpartum. Prepartum heat stress increased 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) concentrations postpartum and increased the rate of uterine involution. Regardless of prepartum treatment, progesterone concentrations indicated that luteal phases had begun by d 12.4 +/- 1.3 postpartum, which was about 3 d before PGFM was basal. The first luteal phase lasted only 10.7 +/- .9 d. First estrus was not detected until d 32.3 +/- 4.8 postpartum. The previously gravid uterine horn had a negative effect on ovarian volume, diameter of the largest follicle and percentage of ovaries with a corpus luteum. However, prepartum heat stress attenuated this effect. This study indicates that heat stress prepartum had residual effects on postpartum reproductive changes, and that the previously gravid uterine horn exerted some control, which was attenuated by heat stress, over ovarian recrudescense. Even though heat stress prepartum affected sensitive measures of postpartum reproductive function, it did not alter days to first estrus, days open (102.3 +/- 13.1) or services/conception (2.5 +/- .3).     

Effect of feeding on reproductive performance in Finnish dairy cows

The effect of 2 types of feeding on the involution of the genital tract and on the fertility was studied in 79 Finnish dairy cows on a research farm. The cows were fed twice a day with home-produced feed in accordance with the Finnish feeding standard. The cows were divided according to the type of feed into a hay-urea group and a silage group. The cows were examined clinically by rectal palpation 3 times a week during 8 weeks postpartum. The time required for the complete involution of uterus and cervix was recorded. The cows in the silage group had a significantly longer time in uterine involution, a lower fertility rate at first insemination and a longer interval from calving to conception than those in the hay-urea group. The pregnancy rate in the first insemination was in the hay-urea group 91% and in the silage group 57%. The interval between calving and the first insemination was shorter in the hay-urea group than in the silage group: 71.4 +/- 10.6 and 74.0 +/- 10.3 days, respectively. The interval between calving and conception was in the hay-urea group significantly (p less than 0.01) shorter than in the silage group; 74.8 +/- 15.1 and 89.5 +/- 24.4 days, respectively.