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.     

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.     

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)     

Effect of postpartum live weight loss on reproductive functions in dairy cows

Postpartum loss of live weight in dairy cows and its association with reproductive functions were studied in a total of 84 (42 Ayrshire and 42 Friesian) cows. 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. All 84 cows were followed during their first postpartum period, 63 during 2 and 57 during 3 consecutive postpartum periods.The resumption of ovarian function was monitored by means of a thrice weekly milk progesterone assay between calving and the first insemination.Live weight changes during the first 30 and 60 days post partum were compared between the 2 breeds and the 2 feed groups.After the second parturition, the mean live weight loss within 30 and 60 days post partum was roughly twice as high (11%) as after the first (4%) and third (6%) carvings. Breed had no significant effect on weight change. The cows in the silage group lost slightly more weight after each parturition than those in the hay-urea group. Low, but statistically significant correlations were noted between weight loss post partum and reproductive functions. The interval from calving to onset of the first visible oestrus was 6 days longer, and to pregnancy 8 days longer in cows which lost more than 10% live weight within 60 days post partum than in those which lost less than 10% (p<0.05). The fertility rate at first insemination (53.1%) was lower in cows which lost more than 10% weight than in those (74.4%) which lost less than 10% (p<0.01). Heat detection rate was not affected by weight loss.     

奶牛子宫复旧期间雌激素与孕酮变化规律的研究

子宫复旧是奶牛产后生殖器官恢复的一个重要时期,复旧时间的长短会直接影响产后第一次发情的时间。本试验为研究雌激素和孕酮在子宫复旧过程中的变化规律,选择了年龄、胎次相近,健康状况良好的产后奶牛15头,应用放射免疫分析法在子宫复旧期间每3d对雌激素、孕酮测定一次,前后持续10次,由试验数据可得出,雌激素、孕酮在子宫复旧早期阶段呈下降趋势,但在18d时浓度都达到了一个峰值,至末期时雌激素水平开始下降,而孕酮水平开始逐渐上升。     

奶牛子宫复旧期间FSH和LH动态变化规律研究

子宫复旧是奶牛产后生殖器官恢复的一个重要时期,复旧时间的长短会直接影响产后第一次发情的时间,子宫复旧的正常时间为产后30～46d。本试验为研究促卵泡素(FSH)与促黄体素(LH)在子宫复旧过程中的变化规律,选择了年龄、胎次相近,健康状况良好的产后奶牛15头,应用放射免疫分析法在子宫复旧期间每3天对奶牛血清中FSH与LH进行一次测定,前后持续10次。由试验数据可得出,FSH与LH分泌水平在子宫复旧的早期比较低,FSH浓度到产后第15天达到峰值,LH从产后第21天开始大幅上升,到产后第24天浓度达到峰值,之后二者浓度变动范围不大。     

Factors influencing conception rate after synchronization of ovulation and timed artificial insemination--a review

This review describes factors that affect conception rate after synchronization of ovulation and timed artificial insemination. Intervals of 7 days between GnRH and PGF2alpha, 48 hours to the second GnRH treatment and a further 16 to 20 hours to the timed insemination have been proven to be most effective. Conception rates (CR) increase as lactation progresses up to 100 days in milk. Primiparous cows have higher CR than older cows. Anovular cows at the start of the synchronization protocols have poor CR. These are highest for cows started in early dioestrus. While poor body condition and some post partum and post insemination health disorders have negative effects on the CR, a significant effect of postpartum chronic endometritis could not be demonstrated. High milk yield was also not shown to have a negative effect on CR in almost all studies, while the negative effect of heat stress on fertility is also found in Ovsynch cows. However, the negative effects of high milk yields and heat stress on AI submission rates are overcome by the timed insemination protocol.     

Onset and duration of luteal activity postpartum and their effect on first insemination conception rate in lactating dairy cows

The incidence of different types of luteal activity postpartum and their effect on reproductive performance were studied in 21 postpartum dairy cows. Progesterone concentrations in defatted milk collected 3 times a week were determined by EIA. Reproductive tract examination was undertaken every other week postpartum. Body weight and body condition score (BCS) were measured before and after calving and the average 100-day milk yield was calculated. Nine (42.9%) cows had normal ovarian activity (first luteal activity < or = 50 days postpartum followed by regular cycles), 5 (23.8%) had prolonged luteal phase (PLP; ovarian cycle with luteal activity > or = 20 days pre-service) and in 7 (33.3%) cows the first luteal activity was shown later than 50 days postpartum (DOV). When compared with normal cows, both PLP and DOV had longer interval to first insemination (63.1 +/- 22.0 days versus 77.6 +/- 21.6 and 93.0 +/- 22.3 days, P<0.05 and P<0.01, respectively), lower first insemination conception rate (88.9% versus 0.0% and 57.1%, P<0.01 and P<0.05, respectively) and greater BCS loss (0.81 +/- 0.2 versus 1.05 +/- 0.21 and 1.04 +/- 0.10, respectively, P<0.01). Cows with PLP showed longer interval to uterine involution than normal and DOV groups (54.0 +/- 8.3 days versus 42.4 +/- 5.5 and 43.3 +/- 8.3 days, respectively, P<0.01) and higher 100-day milk yield (38.8 +/- 2.7 kg versus 33.6 +/- 4.7 and 29.9 +/- 6.1 kg, respectively, P<0.01). In conclusion, more than half of the cows had abnormal luteal activity postpartum, which adversely affected reproductive performance.     

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)     

Relationship between rectal findings of corpus luteum and whole milk progesterone levels in postpartum dairy cows

The reliability of clinical ovarian findings was assessed as an indicator of luteal function in primiparous dairy cows. The postpartum period of 103 cows following their first parturition was studied by thrice weekly rectal palpation of ovaries and whole milk progesterone assay from 1 week after parturition to the first insemination. The relationship between milk progesterone levels and 1101 ovarian findings was compared during the follicular phases, short luteal phases and during the early, mid and late thirds of normal luteal phases. The compatibility between elevated progesterone and palpable corpus luteum was 71%, and between low progesterone and lack of corpus luteum 77%. In 10% of all rectal examinations the finding was unspecified; i.e. the clinician could not differentiate between luteal and follicular activity. During the acyclic period prior to the initiation of luteal function, the proportion of false corpus luteum findings was 11%. The corpora lutea of the short oestrous cycles were more difficult to palpate than those of normal cycles. During early dioestrus the corpus luteum was significantly more difficult to palpate than during the rest of dioestrus. The percentage of unspecified findings was highest during early dioestrus.The paper discusses the reliability of rectal examination as a method of diagnosing cyclicity and of evaluating the responsiveness of a cow to prostaglandin treatment.     

Uterine involution in Finnish dairy cows

The effect of parity on the cervical and uterine involution was studied in 79 Finnish dairy cows on a research farm. The cows were examined clinically by rectal palpation 3 times a week during 8 weeks postpartum. The diameters of the cervix and uterine horns were estimated manually. The parous uterine horn was compared with the non-parous one. The results were separately analysed in primiparous cows (n = 18) and in those with the third calving (n = 61). A significant difference (p less than 0.001) between the parous and non-parous uterine horns was obtained until 21 days. Thereafter, involution still continued and equal diameters for the horns were not found until 5 weeks after parturition. A decline of the cervical diameter continued until 30 days after the delivery. The parity had no significant effect on the swiftness of uterine or cervical involution. However, in multiparous cows the cervical diameter remained larger than that in the primiparous animals still at 8 weeks postpartum.     

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.     

Physiological mechanisms controlling anestrus and infertility in postpartum beef cattle

Postpartum infertility is caused by four factors: general infertility, lack of uterine involution, short estrous cycles and anestrus. The general infertility component is common to any estrous cycle and reduces potential fertility by 20 to 30%. Incomplete uterine involution prevents fertilization during the first 20 d after calving but is not related to anestrus. Short estrous cycles prevent fertility during the first 40 d after calving by causing the cow to return to estrus before pregnancy recognition occurs. Anestrus is the major component of postpartum infertility and is affected by several minor factors: season, breed, parity, dystocia, presence of a bull, uterine palpation and carryover effects from the previous pregnancy as well as two major factors: suckling and nutrition. These major factors have direct effects on anestrus but also interact with one or more other factors to control postpartum anestrus. Physiological mechanisms associated with anestrus involve blockage of the GnRH "pulse generator" in the hypothalamus, but other pathways also must be involved because bypassing the pulse generator is not an effective treatment for all cows. The primary cause of anestrus probably is different for different stages of anestrus. The mediating mechanisms for anestrus are not involved with prolactin, oxytocin, the adrenal or direct neural input from the mammary gland but are at least partially involved with blood glucose and the endogenous opioid peptide system. Management options to decrease the impact of anestrus and infertility include: 1) restrict breeding season to less than or equal to 45 d; 2) manage nutrition so body condition score is 5 to 7 before calving; 3) minimize effects of dystocia and stimulate estrous activity with a sterile bull and estrous synchronization; and 4) judicious use of complete, partial or short-term weaning.     

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.     

The association of ruminal pH and some metabolic parameters with conception rate at first artificial insemination in Thai dairy cows

The objective of this study was to determine the association of metabolic parameters and cow associated factors with the conception rate at first insemination (FCR) in Thai dairy cows. The investigation was performed with 529 lactations from 32 smallholder dairy farms. At 3–6 weeks after parturition, blood samples and ruminal fluid were collected. Body condition scores (BCS) of cows were scored 1 week before expected calving date and at blood sampling date. Ruminal pH was measured at 2–4 h after morning feeding in ruminal fluid collected by ruminocentesis. Serum beta-hydroxybutyrate and serum urea nitrogen were measured by kinetic enzyme method. Cows with first insemination (AI) between 41 and 114 days postpartum were identified after pregnancy diagnosis for FCR. Breed, parity, interval from calving to first AI, BCS before calving, BCS after calving, loss in BCS after calving, SBHB, SUN, ruminal pH, and postpartum problems were selected as independent variables for a model with FCR as a dependent variable. A multivariable logistic regression model was used with farm as a random effect. Overall FCR was 27.2 %. The FCR depended on interval from calving to first AI, BCS before calving, and ruminal pH. The FCR between 69 and 91 days postpartum was significantly highest (45 %). Before calving, a cow with high BCS (≥3.5) had significantly greater FCR than a cow with low BCS (≤3.25; P?<?0.01). An increased ruminal pH raised significantly FCR (OR?=?2.53; P?=?0.03).     

Postpartum follicular and luteal activity in Holstein-Friesian cows genetically selected for high or low mature bodyweight: Relationships with follicle stimulating hormone,insulin, insulin-like growth factor-1 and growth hormone

AIM: To investigate ovarian follicular and luteal activity during the postpartum period of cows genetically selected for high or low mature bodyweight, in relation to metabolic and reproductive endocrine parameters, to determine whether there are differences between strains that could affect fertility outcomes.

METHODS: The presence of follicles ≥5 mm diameter and luteal structures was mapped in the ovaries of 12 high (heavystrain) and 12 low (light-strain) mature bodyweight cows by daily trans-rectal ultrasonography from Day 7 postpartum until the end of their first normal oestrous cycle. Blood samples were collected daily, for measurement of concentrations of follicle stimulating hormone (FSH), progesterone, growth hormone (GH), insulin-like growth factor-1 (IGF-1), and insulin. Intervals to first ovulation were calculated from ultrasonography data.

RESULTS: Heavy-strain cows had shorter intervals than light-strain cows from calving to the emergence of the first (9.0 (SE 0.9) vs 12.4 (SE 1.3) days) and second (16.4 (SE 1.8) vs 20.6 (SE 1.6) days) dominant follicles (p<0.05). Concentrations of FSH in heavy-strain cows prior to the emergence of the second, third and fourth dominant follicles were higher than in light-strain cows (p<0.05). Heavy-strain cows were more likely to have a large (>15 mm diameter) follicle earlier than light-strain cows (p<0.01). Concentrations of insulin and IGF-1, but not those of GH, were higher in heavy- than light-strain cows during the postpartum period (p=0.01 and p=0.02, respectively), and concentrations of both on Day 6 were inversely related to the time of emergence of the first dominant follicle (p>0.01).

Concentrations of progesterone were similar in both strains of cow until Day 10 of the first oestrous cycle, but thereafter were higher in light- than heavy-strain cows until Day 16. Progesterone concentrations in heavy-strain cows declined earlier and more rapidly than in their lighter counterparts.

CONCLUSION: These results indicate that there is a rapid postpartum resumption of follicular activity in both heavy-and light-strain cows, but that there is an earlier emergence of dominant follicles and ovulation in the former. Differences in luteal function, in terms of lower dioestrus progesterone concentrations and an earlier onset of luteolysis, in heavy- than light-strain cows might be sufficient to impair the fertility of the former.     

Relationship between milk somatic cell count and postpartum ovarian cyclicity and fertility in dairy cows

The main objective of the study was to describe the relationship of high somatic cell count (SCC) with the incidence of abnormal postpartum resumption of ovarian cyclicity and reproductive performance in dairy cows. The factors influencing SCC were also investigated. Four hundred and forty-seven cows from six dairy herds in Japan were monitored for SCC and postpartum resumption of ovarian cyclicity. Cows with high SCC (200,000 to 500,000) had a higher incidence of prolonged luteal phase (P < 0.01) than cows with an SCC of 50,000 to 100,000. The high SCC cows (> 500,000) also showed a higher incidence of delayed first ovulation post partum than cows with an SCC ≤500,000 (P < 0.05) during the first month post partum. Cows with an SCC of 200,000 to 500,000 showed lower conception and pregnancy rates, and more days from calving to conception than cows with an SCC of less than 200,000 (P < 0.05). Cows in parity 5 or more had a higher incidence of high SCC than cows in the first and second parities (P < 0.05). It is concluded that cows with a high SCC have a higher incidence of abnormal postpartum resumption of ovarian cyclicity, leading to reduced reproductive performance.     

Effect of Supplemental Feeding with Glycerol or Propylene Glycol in Early Lactation on the Fertility of Swedish Dairy Cows

The aim of this field study was to evaluate the effect of supplemental feeding with glycerol (GLY) or propylene glycol (PG) during early lactation on the fertility of Swedish dairy cows. Within 17 commercial dairy herds, 798 cows were randomized to three groups that were daily fed supplements with 450 g GLY, 300 g PG or nothing (control, C). The supplements were given twice daily during 0–21 days in milk as a top dress on concentrates. Data on calving date, insemination dates, gynaecological examinations, as well as breed, parity and monthly milk yield were collected. From a subset of 308 cows in seven herds, milk samples for progesterone analysis were taken twice weekly and used to determine the time for onset of luteal activity. The effects of supplements on the intervals from calving to first luteal activity (FLA), first AI (FAI) and conception (CON), respectively, were analysed using semi‐parametric survival models (Cox proportional hazards models) controlling for the effect of parity, breed, calving season, milk yield and the clustering effect of herd. There was no difference in time to FLA between the cows in group C and in group GLY or PG. No differences in time to FAI or in time to CON were found between cows in group PG and group C. However, cows in the GLY group tended to get their FAI later compared with cows in the control group but without at subsequent delaying of time to CON.     

Metabolic and luteal function in winter‐calving Spanish beef cows as affected by calf management and breed

This experiment aimed at evaluating the effect of calf management and breed on the metabolic and luteal function of post‐partum beef cows fed at maintenance. Fifty multiparous cows, 22 Parda de Montaña (PA) and 28 Pirenaica (PI), were assigned to either suckling once‐daily for 30 min (RESTR) or ad libitum (ADLIB) from the day after calving. Blood samples were collected to analyse metabolites [non‐esterified fatty acids (NEFA), β‐hydroxybutyrate, total protein and urea)], insulin‐like growth factor‐I (IGF‐I) and progesterone (P4) at different intervals. Cows from RESTR maintained their live‐weight (LW) over the first 3 months post‐partum, whereas ADLIB cows lost nearly 4% LW. Both genotypes showed similar LW gains during this period (p > 0.10). Calf daily gains were lower in RESTR than in ADLIB treatment (p < 0.05), but similar across breeds (p > 0.10). Milk and lactose production were lower in RESTR cows than in ADLIB (p < 0.05). Milk and protein yield were greater in PA than in PI breed (p < 0.05). Serum NEFA, total protein and urea were higher in PI cows suckling ADLIB than in the rest (p < 0.05). Cows from PI breed had greater NEFA values than PA ones on the first week post‐partum (p < 0.001). Circulating IGF‐I was not affected by suckling frequency, breed nor their interaction (p > 0.10). Suckling frequency, but not breed, affected the interval from calving to first ovulation (p < 0.001), being shorter in RESTR than in ADLIB cows. In conclusion, the ad libitum suckling practice improved cow milk yield and offspring gain compared to once‐daily suckling for 30 min from the day after calving, at the expense of impairing the onset of cyclicity. The effect of calf management was confounded with breed on the studied blood biochemical constituents, but any of these metabolites influenced the role of endocrine IGF‐I in these genotypes.