Induction of Lactation by Two Techniques: Success Rate,Milk Composition,Estrogen and Progesterone in Serum and Milk,and Ovarian Effects

Induction of lactation was attempted in 12 heifers and 12 cows with estradiol benzoate (.011 mg/kg body weight per day) subcutaneous for 10 days or that plus progesterone (.1 mg + .25 mg/kg body weight per day) for 7 days. Milking commenced on day 20 for those treated with the mixture and on day 11 for the others. Lactations were induced (minimum of 4.5 kg of milk/day) in five of six heifers and two of six cows by the mixture and in six of six heifers and three of six cows for estradiol benzoate. Milk production was 44% of herdmates in the 16 induced lactations. Cows on the single treatment had lower production than the other three groups. Ovarian status, cycling, cystic, or static, was affected adversely in 5 of 16 animals induced successfully. Two of the 16, both heifers, carried calves to term following induction. The transition to normal composition of milk was slower for single than double treatment. Lactose increased slowly to normal over the 1st wk of milking while protein decreased slowly. Estrogen and progesterone in milk of induced cows were approximately twice as concentrated as in normal post-parturient cows, probably because milk production was halved.     

Expression of the insulin-like growth factor (IGF) system in the bovine oviduct at oestrus and during early pregnancy

Early mammalian embryo development in vitro can be enhanced by co-culture with oviductal cells and by the addition of insulin-like growth factors (IGFs). This study examined the expression patterns of the oviductal IGF system in cattle in relation to the number of days after oestrus and the presence or absence of embryos. Oviducts were collected from: (i) 66 nulliparous heifers on day 3, day 6 or day 16 after insemination and from (ii) ten non-pregnant, lactating cows on day 0 or day 1 of the oestrous cycle. Oviducts were coiled, frozen whole and sectioned for in situ hybridization. Expression patterns of mRNAs encoding IGF-I, IGF-II, type 1 IGF receptor (IGF-1R), and the IFG binding proteins (IGFBP)-1, -3 and -5 were determined from autoradiographs. Separate measurements were made for the mucosa and muscle layers of the infundibulum, ampulla and isthmus. None of the parameters measured differed between heifers with or without the presence of an embryo. mRNAs encoding IGF-I and IGF-1R were present in the mucosa and muscle of all three oviductal regions, and the highest value of IGF-I mRNA was measured in heifers on day 3. IGF-II mRNA was expressed predominantly in the muscle wall. IGFBP-1 mRNA was not detectable, whereas mRNAs encoding IGFBP-3 and -5 were expressed in both the muscle and mucosa. IGFBP-3 expression was higher in cows on day 0 and day 1 of the oestrous cycle than in heifers on day 3, day 6 and day 16 after insemination. A peak of IGFBP-5 expression was reached on day 6. Locally or systemically produced IGFs, regulated by IGFBPs, may act directly on the embryo or indirectly via modulation of oviductal secretions and muscular activity to influence the success of early embryo development.     

Effect of monopropylene glycol on luteinizing hormone, metabolites, and postpartum anovulatory intervals in primiparous dairy cows

This study examined the effect of monopropylene glycol (MPG) supplementation on LH secretion, postpartum interval to first ovulation, and milk production in heifers calving with poor body condition score (BCS). Forty-seven heifers were allocated to 3 treatments: 1) heifers with high BCS (BCH; n = 13) that calved at a BCS of 3.4 (BCS scale of 1 to 5); 2) heifers with low BCS (BCL; n = 17) that calved at a BCS of 2.8; and 3) heifers with low BCS that calved at a BCS of 2.8 and were assigned to receive MPG supplementation (BCL + MPG; n = 17) and grazed pasture ad libitum. Monopropylene glycol was drenched (250 mL) twice daily for 16 wk after calving. Patterns of change in plasma LH were measured at 2 and 5 wk after calving. Pulsatile release of LH at 2 and 5 wk was greater in BCL + MPG and BCH cows compared with the BCL control cows. The BCL + MPG cows had lower NEFA concentrations than did the BCL cows during wk 1 to 6 after calving. At 12 wk postpartum, the proportion of cows cycling was 77, 82, and 28% for the BCH, BCL + MPG, and BCL treatments, respectively. Mean milk fat yield was greater for the BCH treatment during the first 12 wk postpartum compared with the BCL + MPG or BCL treatments, which did not differ from each other. Results of this study indicate that MPG supplementation reduced the interval from calving to first ovulation in heifers having poor body condition at calving.     

Relationships between reproductive traits of heifers and cows and yield traits for Holsteins in Japan

The objective of this study was to investigate relationships between reproductive traits in heifers and cows and yield traits for Holsteins in Japan. Insemination and lactation records for cows calved between 1990 and 2003 in Hokkaido region were obtained. Age at first service, age at conception, and conception rate for first service were calculated for heifers. Days from calving to first service, days open, and conception rate for first service were calculated for first- and second-parity cows. The yield traits used were 305-d milk, fat, and protein yields. A threshold animal model was applied for the conception rate for first service, and a linear animal model was applied for the other traits. Single-trait and 2-trait genetic analyses were performed by the Bayesian method using Gibbs sampling. Heritability estimates ranged from 0.027 to 0.051 for conception rate for first service, and from 0.074 to 0.128 for the other reproductive traits. If the relationships of other traits were not considered, days from calving to first service was favorable to genetic selection for reproductive traits because of relatively high heritability and because it can be available earlier than the days open. Genetic correlations among reproductive traits were high, especially in cows. The genetic correlations between reproductive traits for heifers and those for cows were lower than the genetic correlations between reproductive traits for first parity and those of second parity, suggesting that reproductive traits for heifers should be evaluated separately from reproductive traits for cows. Genetic correlations between yield and reproductive traits in cows were antagonistic. In contrast, genetic correlations between reproductive traits for heifers and yield traits were slightly desirable. Depending on the reporting rate of insemination records for heifers and the results of investigations for relationships with productive maturity, selection by reproductive traits for heifers will enable the improvement of reproductive performance without a loss in genetic progress for yield traits.     

Changes of aldosterone in blood serum of dairy cattle during estrous cycle

Blood samples were taken daily from five lactating cows and five open heifers beginning with the 1st day postestrus and continuing until the animal was observed in standing estrus. Means of aldosterone in blood serum were 102.6 +/- 5.1 pg/ml for lactating cows and 94.1 +/- 5.1 pg/ml for open heifers. Age and lactation did not appear to be major factors affecting circulating aldosterone in the bovine species. Effect of day of the estrous cycle on aldosterone was quadratic. Concentrations of aldosterone for lactating cows started at 92.3 pg/ml on day 1 of the estrous cycle, peaked at 125.5 pg/ml on day 8, then declined steadily to a low of 43.2 pg/ml on day 20. There was no significant interaction of group by day. During the estrous cycle aldosterone appeared to be related to development of corpus luteum and progesterone. Sodium in blood serum was higher during estrus for lactating cows than open heifers for linear, quadratic, and cubic effects. Although not correlated with aldosterone, sodium exhibited similar cyclic patterns throughout the estrous cycle. Responses between sodium and aldosterone appeared delayed during estrus.     

Effect of prepartum photoperiod and melatonin feeding on milk production and prolactin concentration in dairy heifers and cows

Holstein multiparous cows (n = 29) and primiparous heifers (n = 32) calving over a 1-yr period were subjected to photoperiod-melatonin treatments according to a 2 × 3 factorial design. Starting 8wk before expected calving, all animals were subjected to 1 of the following treatments: 8h of light and 16h of dark (8L:16D), 16h of light and 8h of dark (16L:8D), or 16L:8D plus melatonin feeding (16L:8D-melatonin). Each day at 1355h, the animals in the melatonin treatment received orally a gelatin capsule containing 25mg of melatonin. The treatments ended at calving, when the animals were moved to the lactation barn; all animals were then subjected to about 16h of light per day. At the beginning and end of the treatment period before calving, blood samples were taken from 6heifers and 6cows through a jugular cannula for 24h at 30-min intervals to monitor serum melatonin and prolactin concentrations. Milk production in the heifers was not affected by the photoperiod treatments. Early-lactation milk production was higher in the cows exposed to the short-day photoperiod than in those exposed to a long-day photoperiod (16L:8D and 16L:8D-melatonin), with averages of 36.7 ± 0.9, 33.1 ± 0.8, and 34.1 ± 0.9kg/d for 8L:16D, 16L:8D, and 16L:8D-melatonin, respectively. Photoperiod had no effect on late-lactation milk production in the cows. During lactation, the dry matter intake of heifers was not affected by the treatments, but dry matter intake of the cows exposed to a short-day photoperiod was greater than that of the cows exposed to a long-day photoperiod. Feed efficiency of heifers was improved by short-day photoperiod. During the treatment period, prolactin concentration was lower in the animals exposed to a short-day photoperiod than in those exposed to a long-day photoperiod, was lower with the 16L:8D-melatonin treatment than with the 16L:8D treatment, and tended to be lower with the 8L:16D treatment than with the 16L:8D-melatonin treatment, with averages of 3.5 ± 0.8, 9.9 ± 0.8, and 6.0 ± 0.8ng/mL for 8L:16D, 16L:8D, and 16L:8D-melatonin, respectively. In early lactation, prolactin concentration was lower in the heifers exposed to the 16L:8D photoperiod during the dry period than in those exposed to the 8L:16D photoperiod or fed melatonin. In conclusion, a short-day photoperiod during the dry period transiently increases milk production of cows and the feed efficiency of heifers in the following lactation. However, melatonin cannot be used to mimic a short-day photoperiod during the dry period.     

Short communication: Evaluation of vaginal discharge following treatment with a progesterone insert

Yellowish discharge after application of intravaginal progesterone releasing inserts is frequently observed in cows. The objective of this study was to compare the bacteriological contamination of the vagina and uterus before and after a treatment with a progesterone insert in heifers. Forty-two Holstein heifers received a progesterone releasing insert [Eazi-Breed controlled internal drug release (CIDR) insert; Pfizer Animal Health, Berlin, Germany] for 7d. The protruding tail had been removed from half of the inserts (no tail group: n=21; tail group: n=21). Nine heifers from the tail group lost the insert within the 7-d treatment interval and were excluded. Heifers identified in estrus were artificially inseminated on d 9 or 10. Vaginal discharge was scored on a 4-point scale [vaginal discharge score (VDS) 0 to 3] and vaginal swabs were taken for bacteriological examination on d 0 and 7 and the day of artificial insemination (AI). Furthermore, cytological and bacteriological samples were obtained from the uterus on d 7 and the day of AI. On d 0, coliforms and Streptococcus spp. were found in vaginal swabs of 21 heifers (64%). On d 7, all heifers showed purulent vaginal discharge (VDS 2 to 3). The VDS was higher in the tail group compared with the no tail group. Arcanobacterium pyogenes, coliforms, and Streptococcus spp. were isolated from the vaginal swabs in 32 of 33 (96%) heifers on d 7. On the day of AI, VDS had improved to 0 or 1 in 96% of the heifers. However, A. pyogenes, coliforms, and Streptococcus spp. were still isolated in 17 of 33 (53%) heifers from the vagina and in 32 of 33 (96%) heifers from the endometrium. Endometrial cytology revealed polymorphonuclear neutrophils (PMN) in 11 heifers (6 to 32% PMN). Five samples exceeded the threshold of 5% PMN, and 2 samples exceeded the 10% PMN threshold, indicative of subclinical endometritis. In conclusion, pyogenic bacteria were found in the vagina and uterus on d 7 and the day of AI after intravaginal progesterone treatment. The severity of the discharge was affected by the protruding tail of the insert.     

A descriptive study of the survival of Holstein-Friesian heifers through to third calving on English dairy farms

A short herd lifespan severely limits opportunities for on-farm selection of breeding cows in addition to causing financial losses on dairy farms and presenting welfare issues for individual animals. This prospective study monitored survival up to third calving and reasons for culling of a cohort of 468 Holstein-Friesian heifers on 18 dairy farms across southern England. Heifers born during 2003 and 2004 were monitored from 1 mo of age through to third calving. A longevity index was calculated as the proportion of days alive spent in milk production, a good measure of lifetime performance. On average, 11% of heifers recruited at 1 mo did not survive until first calving (0% longevity index). Of those that did calve, 19% were culled in lactation 1 (total average lifetime days in milk of 322 with a longevity index of 24%) and 24% were culled during lactation 2 (total average lifetime days in milk of 623 with a longevity index of 40%). The primary cause for culling was infertility. Only 55% of replacement heifers calved successfully for a third time, ranging from 80 to 32% across individual farms. These results show that on a selection of UK farms, a large number of heifers never become productive or are culled before they reach their full lactation potential. Increasing the productive lifetime of dairy cows would improve the efficiency of dairy production by lowering replacement costs and capturing a greater proportion of potential lactation milk yield from mature cows.     

Comparison between low-dose,high-sort and high-dose,low-sort semen on conception and calf sex ratio in Jersey heifers and cows

The objective of this clinical trial was to compare conception and newborn calf sex ratios among Jersey heifers and lactating cows inseminated with either standard sex-sorted semen (low-dose, high-sort; LDHS) containing 2.1 × 10⁶ sorted sperm at 90% purity or high-dose, low-sort (HDLS) semen containing 10 × 10⁶ sorted sperm at 75% purity. After a specified voluntary waiting period (VWP), female subjects, consisting of nulliparous heifers (VWP 10 mo of age) and lactating cows (VWP 50 d in milk), received their first service and were systematically allocated to each treatment group in the order in which they presented for artificial insemination (AI). Females were bred to the same sire and type of sex-sorted semen for up to 2 additional services. Animals that were not pregnant after 3 breeding attempts were excluded. A total of 1,846 services were performed on 1,011 eligible females (LDHS; n = 494, HDLS; n = 517), which consisted of 516 nulliparous heifers and 495 lactating cows. Study groups were comparable with respect to the mean age at first AI for nulliparous heifers and the mean days in milk at first AI for parous cows. Insemination with HDLS semen did not result in a higher proportion of pregnancies per AI (P/AI) compared with LDHS semen for either nulliparous heifers (P/AI = 43 vs. 38%) or parous cows (P/AI = 47 vs. 43%). Insemination of nulliparous heifers using HDLS resulted in a lower proportion of newborn female calves compared with those bred to LDHS (76% vs. 87%). Similarly, lactating cows bred to HDLS gave birth to a lower proportion of newborn female calves compared with those bred to LDHS (79 vs. 90%). The odds ratio for a female calf to be born to an animal inseminated with HDLS compared with LDHS was 0.32 for nulliparous heifers and 0.19 for parous cows. Overall, the use of HDLS resulted in fewer females compared with LDHS, which may be explained by the lower concentration of X-bearing spermatozoa in HDLS compared with LDHS.     

Influence of milking frequency on productive and reproductive efficiencies of dairy cows

Thirty-four mature Holstein cows were blocked into two groups on their 305-day, twice daily milked, mature equivalent milk production of the previous lactation; groups were assigned at random to a twice or thrice daily milking frequency. In addition, six pairs of paternal half-sisters and one pair of nonsibling heifers also were assigned to twice daily or thrice daily milking frequency. Half-sisters were assigned to milking frequency on alternate calvings, and the nonsibling pair was assigned at random. Milk production peaked at 6 wk lactation in mature cows in both treatments, at 7 wk for cows in first lactation milked twice daily, and at 9 wk for cows in first lactation milked thrice daily. Cows milked thrice daily reached higher peak milk production and were more persistent in milk production. Multiparous and first-lactation cows milked thrice daily produced 18.5 and 25.2% more milk than their counterparts milked twice daily, and after 15 wk heifers milked thrice daily were producing more milk per day than mature cows milked twice daily. The combined increased average production for cows and heifers milked thrice daily, 1299 kg, required only 92 kg more dry matter intake and resulted in an apparent preferential utilization of feed nutrients for milk production or higher rate of tissue catabolism in cows milked thrice daily. Milk composition was not influenced by milking frequency; total milk fat was 36 kg more for cows milked thrice daily. Reproductive performance measured as days to first estrus, days open, or services per conception also was not influenced by milking frequency.     

Evaluation of potential carryover effects associated with limit feeding of gravid Holstein heifers

Ninety-six Holstein heifers (400 ± 6 kg, 15.2 ± 0.1 mo), including 9 with ruminal cannulas, were offered 1 of 3 diets for 180 ± 8 d in a randomized replicated pen design. Dietary treatments included a control diet (C100) and 2 independent limit-fed (LF) diets. The LF diets included one offered at 85% of C100 intake (L85) without an ionophore, and a second containing an ionophore (325 mg/head per day of lasalocid) that was offered at 80% of C100 intake (L80+I). Heifers were evaluated for growth, rumen digesta volume, nutrient excretion, and subsequent lactation performance. Limit-fed heifers consumed less dry matter and neutral detergent fiber, and had greater respective average daily gains (0.96 or 0.89 vs. 0.81 kg/d), and lower feed:gain ratios (9.1 or 9.3 vs. 13.0 kg/kg) compared with heifers offered the C100 diet. No differences in rumen pH, NH₃-N, or volatile fatty acid concentrations were observed between C100 and LF heifers. Rumen digesta volume, density, and weight were unaffected by LF, and feeding L85 or L80+I did not result in carryover effects for rumen digesta volume when these heifers were offered a common high-fiber diet immediately after the 180-d growth trial. At parturition, no differences were observed for dystocia index, calf body weight, or 7-d postpartum body weight between cows offered LF or C100 diets as heifers. Lactation body weight, dry matter intake, and feed efficiency of cows did not differ between treatments at 45 or 90 d in milk. Milk yield and milk components also were not different between cows that were offered C100 or LF diets as gravid heifers. At 45 d in milk, rumen digesta volume was greater (99.1 vs. 66.1 L) for cows offered L85 compared with cows offered L80+I as gravid heifers, but this effect was not observed at 90 d in milk. Limit feeding of gravid Holstein heifers for 180 d did not result in any carryover effects during their first lactation for rumen digesta volume, dry matter intake, or milk yield.     

Quality of embryos produced from dairy cows fed whole flaxseed and the success of embryo transfer

The objective of the experiment was to determine the effects of fat supplementation on embryo quality of dairy cows and the subsequent success of embryo transfer into recipient heifers fed the same sources of fat. A total of 30 lactating Holstein cows were allotted on d 18 postpartum to 2 groups of 15 donor cows blocked for similar calving dates. Total mixed diets based on silage and fat supplements were fed for ad libitum intake. On a dry matter basis, diets fed to donor cows contained 7.9% whole flaxseed or 2.8% calcium salts of palm oil and those fed to recipient heifers contained 11.4% whole flaxseed or 4.2% calcium salts of palm oil. The experiment with donor cows was carried out between d 18 and 109 of lactation. The experimental diets were fed to 121 recipient heifers from wk 8 before estrus synchronization and superovulation to d 50 of gestation. Dietary fat fed to donor cows had no effect on the number of viable embryos per cow (3.7 ± 0.5), the number of degenerated embryos per cow (1.8 ± 0.4), or the number of unfertilized oocytes per cow (2.1 ± 0.8). But feeding flaxseed decreased fertilization rate (64.3 vs. 78.4%) and the percentage of grade 1 to 2 embryos (56.5 vs. 74.1%) and increased the embryo degeneration percentage (27.4 vs. 18.2%) compared with feeding calcium salts of palm oil. There was no effect of diets fed to donor cows and those fed to recipient heifers for pregnancy rate of heifers. Supplementation with a rich source of n-3 fatty acids decreased quality of embryos from donor lactating dairy cows compared with feeding calcium salts of palm oil, but had no effect on the subsequent pregnancy rate of heifers receiving frozen grade-1 embryos.     

Pregnancy incidence in Norwegian red cows using nonreturn to estrus, rectal palpation, pregnancy-associated glycoproteins, and progesterone

The objectives of the study were to estimate pregnancy incidence and calving rate after first artificial insemination (AI) in Norwegian Red cows undergoing spontaneous estrus, to assess the relationship between pregnancy and management factors at herd or cow level, to evaluate differences between 60-d nonreturn rate (NRR60d) and pregnancy incidence, and to compare the accuracy of pregnancy diagnosis by rectal palpation and plasma pregnancy-associated glycoproteins (PAG) analysis supported by progesterone measurements. In total, 829 animals (n = 229 heifers, 234 first-lactation, 173 second-lactation, and 193 >second-lactation cows) were included. Milk samples for progesterone analysis were collected both at AI and 3 wk later. Cows with progesterone concentrations <3 ng/mL at AI were considered in estrus or having nonactive ovaries, whereas cows with progesterone concentrations >7 ng/ mL 3 wk later were considered pregnant. Blood sampling for PAG analysis and pregnancy diagnosis by rectal palpation were conducted 57.6 ± 0.92 d after AI. Pregnancy-associated glycoprotein concentrations equal to 2.5 ng/mL gave the greatest sensitivity (94.3%) and specificity (94.6%) in the assessment of pregnancy. The number of days from calving to first AI was 85.3 ± 1.71. Overall NRR60d after first AI was 72.5%. The corresponding values for heifers, first-lactation, second-lactation, and >second-lactation cows were 76.9, 67.1, 69.9, and 76.2%. Overall pregnancy incidence after first AI was 63.7%. The corresponding values for heifers, first-lactation, second-lactation, and >second-lactation cows were 70.0, 58.2, 61.6, and 64.9%. Overall calving rate to first AI was 57.2%. The corresponding values for heifers, first-lactation, second-lactation, and >second-lactation cows were 64.9, 54.3, 54.7, and 53.9%. The overall difference between NRR60d and pregnancy incidence was 8.8%, whereas the parity-specific differences were 6.9, 8.9, 8.3, and 11.3% for heifers, first-lactation, second-lactation, and >second-lactation cows, respectively. Eight animals with PAG <2.5ng/mL and classified as pregnant by rectal palpation calved, whereas 5 animals with PAG ≥2.5 ng/mL and classified as non-pregnant by rectal palpation also calved. The study showed that Norwegian Red cows have relatively high reproductive performance. Breeding for fertility traits over 35 yr is probably an important reason for such high fertility.     

Interrelationships With Estrous Behavior and Conception in Dairy Cattle

A total of 199 inseminations and estrous periods of lactating cows and heifers of breeding age were used to assess behavioral, productive, environmental, and hormonal events at first observation of estrus and those 12 h later with concurrent breeding efficiencies. Cattle were observed twice daily for estrus, and blood samples were collected at the initial observation of estrus (0 h) and at 12 h. Fifty-one percent of the cattle first were detected in estrus in the morning. Morning estrous activity was greater (11.4 mounts/h) than that first observed in the evening (7.6). Mean estrous activity declined from 9.4 mounts/h at 0 h to 1.6 mounts/h at 12 h. Older cows exhibited more mounting activity than younger animals at 0 h. Barn housed cattle exhibited more mounts/h during detection of estrus (11.2) than cattle housed primarily in free stalls (6.5) or pasture (5.4). Early estrous activity (0 h) was not affected by estradiol, progesterone, or luteinizing hormone. However, estradiol and progesterone did exert an influence on activity seen at late estrus (12 h). Glucose and urea at 0 and 12 h were similar. There were no significant correlations of glucose or urea of plasma with estrous activity or conception. Feed intake and milk production from 3 days prior to 3 days postestrus did not change. Season affected estrous activity and conception. Highest conception was associated with low progesterone at 12 h.     

Response of Cows Consuming Adequate Selenium to Vitamin E and Selenium Supplementation Prepartum

A 2-yr study of 195 parturitions was to evaluate the prepartum need for supplemental vitamin E and selenium by cows consuming diets that contained ample amounts of selenium (.1 to 2.0 ppm selenium). One-half of the cows were injected with 68 IU vitamin E and 5 mg selenium per 45.4 kg body weight approximately 21 days prepartum. Incidences of retained placenta and calving difficulty were similar for treated and control cows. There was a lower incidence of retained placenta (7.5%) for cows that calved during fall, whereas incidence was greater than 20% in cows that calved during the rest of the year. Serum vitamin E and selenium concentrations in treated cows doubled within a day after injection, then declined to concentrations typical of untreated cows within 8 and 3 days postinjection, respectively. Serum carotene, vitamin A, and vitamin E concentrations were similar for treated and control cows and were elevated in cows that calved during the summer and fall, possibly because cows dry during the grazing season were pastured. However, discriminant analysis of 21-day prepartum serum data indicated that serum concentrations of carotene, vitamins A or E, or selenium would not predict accurately the retention of the placenta. Colostrum and 4-day milk from treated and control cows contained similar amounts of vitamin E and selenium.     

Breeding Practices on Selected North Carolina Dairy Farms

In 1978, 147 North Carolina dairy farms were surveyed concerning their breeding practices. Average herd size was 121 cows (range 24 to 440). Of 17,773 cows 78.5% and of 4,300 heifers 25.5% were bred by artificial insemination. Approximately 25% of dairymen indicated they had increased artificial insemination in the past 3 yr, whereas 12% reported less. A bull was used on 88% of farms. Herds having the same number of cows but using 100% artificial insemination on the milking herd averaged more days open (13.3), longer calving intervals (.44 mo), and more cows leaving the herd because of reproductive problems (8.3% vs. 5.8%) compared to herds using 80 to 99% artificial insemination. Herds using 0 to 75% artificial insemination were intermediate between the two. Herds using 100% artificial insemination and those using 80 to 99% averaged 7050 kg milk and 1.8 services per conception. Herds using 0 to 75% artificial insemination had lower milk production (480 kg). Larger herds had lower reproductive performance. Herds with higher average milk production had more services per conception. Average estimated transmitting abilities of 88 natural service sires were 371 kg milk, ?.05% fat and 10 kg fat.     

Influence of cortisol and dexamethasone on estrous behavior of estradiol-treated ovariectomized cows and heifers

Two experiments were conducted with estradiol-treated ovariectomized cows and heifers to determine if cortisol and dexamethasone inhibit estrous behavior. In Experiment 1, eight ovariectomized Holstein cows were subjected to weekly hormonal treatments in a replicated 4 X 4 Latin square. Treatments consisted of 500 micrograms estradiol benzoate and either 0, 40, 80, or 160 mg cortisol. During the 48 h after hormonal injection, 2-h periods of observation were alternated with 2-h periods of no observation. During each observation period, cows were observed continuously for 14 behavioral interactions that increase in frequency at estrus. Percentage of cows exhibiting estrus, interval from injection of hormones to the onset of estrus, duration of estrus, and total numbers of each behavioral interaction were similar for all treatments. In Experiment 2, 10 ovariectomized Holstein heifers were subjected to weekly hormonal treatments in a replicated 5 X 5 Latin square. Treatments consisted of 500 micrograms estradiol benzoate and either 4 mg dexamethasone, 0, 50, 100, or 200 mg cortisol. The estradiol benzoate plus dexamethasone treatment tended to lower the percentage of cattle exhibiting estrus. Interval from injection to onset of estrus, duration of estrus, and total numbers of each behavioral interaction were similar for all treatments. These data indicate that cortisol given with estradiol did not inhibit estrus in ovariectomized cows and heifers, whereas dexamethasone tended to inhibit induced estrus.     

Estrous cycle patterns in cattle monitored by electrical resistance and milk progesterone.

An electronic probe with parallel stainless steel electrodes was designed to measure changes in electrical resistance in the anterior vagina associated with increased cervical mucus secretion at estrus. Three groups of Holsteins were probed, and a sample of residual milk after milking was taken for progesterone assay every 2nd day for 28 to 40 days. Group I consisted of 29 cycling virgin heifers, Group II consisted of 24 lactating cows in the Cornell herd, and Group III consisted of 62 lactating cows in three commercial herds. Lactating cows were 26 or more days postpartum when sampling began. In Group I, 77% of the measurements at the ventral surface of the anterior vagina were lowest on the day of estrus and correlated well with days KaMaR Heatmount Detectors were triggered or chalk was erased. In Groups II and III, average electrical resistance also was minimal at estrus and was correlated .92 to .99 with average milk progesterone during the 4 days preceding and including estrus. The electronic probe appears to enable one to detect which cows are cycling normally and to aid in determining when to expect estrus.     

Effects of polybrominated biphenyls on health and performance of pregnant Holstein heifers.

The toxicity of a commercial blend of polybrominated biphenyls was determined in 24 pregnant Holstein heifers that were allotted randomly to one of four experimental groups given 0, .25, 250, or 25,000 mg/day of fire-Master BP-6. The polybrominated biphenyls were mixed with finely ground corn and given by bolus for 60 days or until the animal became moribund. Average body weight of heifers at onset of experiment was 381 kg. No clinical signs of toxicosis were evident in heifers fed 0, .25 or 250 mg/day. Toxicosis was induced in heifers fed 25,000 mg/day resulting in reduced dry matter intake, body weight, heart rate, and respiration rate. Clinical signs were anorexia, emaciation, dehydration, excessive lacrimation and salivation, diarrhea, depression, and abortion or fetal death. All heifers fed 25,000 mg/day became moribund within 33 to 66 days.