Timing of insemination for dairy cows identified in estrus by a radiotelemetric estrus detection system

The optimal time of artificial insemination (AI) was determined from data for 2661 AI in 17 herds utilizing a radiotelemetric system for estrus detection that has the potential for continuous 24-h surveillance to monitor behavioral events associated with estrus. The system consisted of pressure-sensitive radio frequency transmitters affixed over the sacrum region of cows. The activation of the sensor sent a radiotelemetric signal to a microcomputer via a fixed antenna. Cow identification, date, time, and duration of each standing event were recorded in the software program provided with the system. Each farm selected a 3-h interval to AI for cows that were identified in estrus during the previous 24 h. Pregnancy status was determined from data for return to estrus and palpation of the uterus 35 to 75 d following AI. Standing events during estrus averaged (+/- SD) 8.5 +/- 6.6 per cow, and the number of events per estrus across herds averaged from 6.2 +/- 5.1 to 12.8 +/- 9.9 per cow. The duration of estrus ranged from 5.1 +/- 3.8 to 10.6 +/- 6.8 h across herds; the mean was 7.1 +/- 5.4 h. The interval from the first standing event to AI affected the probability of pregnancy; the highest conception rates for AI occurred between 4 and 12 h after the onset of standing activity. The probability of pregnancy was higher for cows > 100 d in milk, exhibiting > 2 standing events during estrus, and inseminated during March, April or May.     

The effect of artificial insemination once versus twice per day

The objective of this study was to determine the effect of inseminating Jersey cows and heifers once per day or according to the a.m.-p.m. rule. A total of 337 artificial inseminations (AI) were completed by three technicians at the University of Tennessee Dairy Experiment Station at Lewisburg for 6 mo. Cows and heifers were inseminated at estrus using the a.m.-p.m. rule on even days of the month. On odd days of the month, AI were once daily between 0800 and 1200 h. Estrus detection was conducted two to three times daily. Pregnancy was confirmed by rectal palpation 60 to 80 d after AI. Herd DHIA averages were a 12.2-mo calving interval, 76 d to first AI, 83% observed estruses, and a 50% conception rate during the trial. Pregnancy data were analyzed with a model including treatment, AI, lactation number, parity, technician, and group. This study grouped cows and heifers according to when they were in estrus and inseminated (a.m.-a.m., a.m.-p.m., or p.m.-a.m.); means were 43.7, 57.9, and 59.0%, respectively. The a.m.-p.m. AI versus once per day AI yielded a pregnancy rate of 55.6% versus 51.3%. These results show no difference among Jersey cows or heifers that were inseminated artificially once daily in the a.m. However, those cows and heifers inseminated in the a.m. of first estrus detection had a lower pregnancy rate.     

Development of a progestin-based estrus synchronization program: II. Reproductive response of cows fed melengestrol acetate for 14 days with injections of progesterone and prostaglandin F2alpha

We tested the efficacy of an estrus control system designed to provide optimal control of follicular development. In Exp. 1, postpartum cows (n = 133) and yearling heifers (n = 57) were fed either .5 mg x female(-1) x d(-1) of melengestrol acetate (MGA) or the carrier for MGA from d -13 to d 0 (d 0 = last day of MGA feeding). All females received 25 mg of PGF2alpha (i.m.) on d -13 and 0. On d -6, cows and heifers fed MGA were administered an i.m. injection of progesterone (200 mg; MGA/P4), and those fed the corn carrier (2XPGF2alpha) received no progesterone. Beginning on d 1, females were bred by AI from d 1 to at least d 5. During the estrus synchronization period (d 1 to d 5), more (P < .05) postpartum cows were observed in estrus (70.1 vs 42.4%), the timing of estrus was more (P < .05) precise, conception rate was similar, and pregnancy rate was higher (P < .05) in the MGA/P4 than in the 2XPGF2alpha treatment. More (P < .05) cows that were anestrous at the beginning of the breeding season were in estrus during the synchronization period in the MGA/P4 (55.8%) than in the 2XPGF2alpha (28.6%) treatment. In heifers, estrus was synchronized in over 90% of females, and neither conception nor pregnancy rate during the synchronization period differed between treatments. In Exp. 2, postpartum cows (n = 122) and heifers (n = 84) received treatments (MGA/P4 or 2XPGF2alpha) as described for Exp. 1 with one exception. In the MGA/ P4 treatment, progesterone was administered on d -7 rather than d -6. Females were bred by AI from d 1 to 5. The estrus response and conception rate during the synchronization period did not differ between treatments for either cows or heifers. We conclude that the progestin-based estrous synchronization system used in this study effectively synchronized an estrus of normal fertility in cyclic cows and induced a majority of anestrous cows to reinitiate estrous cycles.     

Timing of artificial insemination of dairy cows: fixed time once daily versus morning and afternoon

Nonreturn rates to professional technician service of 7240 first AI Holstein cows were calculated to evaluate differences between once daily and a.m.-p.m. AI. To determine whether management practices affected nonreturn rates, participating herd owners were surveyed for methods used for detection of estrus. Nonreturn rates for once daily and a.m.-p.m. AI were 64.6 and 65.6% for 60-d, 60.1 and 60.6% for 75-d, and 58.4 and 57.8% for 90-d nonreturn periods. Signs of estrus for AI and interval from detection of estrus to AI were related to nonreturn rates. Nonreturn rate was highest, 63.4%, when cows were in standing estrus. Nonreturn rates were lowest, 36%, when cows were bred after treatment with PGF2 alpha without being detected in estrus or bred strictly on veterinary advice based on palpation. Nonreturn rates were similar for different times of the day when once daily AI was practiced. However, AI in the midmorning may have some advantages. The highest nonreturn rate for a 3-h period was 68.2% for 0800 and 1100 h; the lowest was 54.7% for 1300 to 1600 h. Movement before observation for estrus and an observation period > 15 min improved nonreturn rates for once daily AI. Once daily AI can be used effectively with no difference from the traditional a.m.-p.m. system; results are best when AI is based on standing estrus and performed between 0800 and 1100 h.     

Effect of norgestomet treatment after insemination on the calving rate of postpartum suckled beef cows

Two experiments were conducted on postpartum suckled beef cows synchronized with Syncro-Mate B and artificially inseminated approximately 48 h after implant removal. In Exp. 1, cows (> or = 42 d postpartum at the timed AI) were randomly assigned to treated (n = 101) and control (n = 85) groups on d 12 after the timed AI. Treated cows received norgestomet/silicone implants that were left in situ for 9 d. Norgestomet treatment had no effect (P > .25) on the calving rates from the initial timed AI or from the return estrus. Nonpregnant norgestomet-treated cows returned to estrus in a more (P < .05) synchronized manner than the nonpregnant control cows. In Exp. 2, early postpartum cows (< 42 d postpartum at the first AI; n = 30) were included and all 118 cows (88 cows were > or = 42 d postpartum) received norgestomet/silicone implants as in Exp. 1. Of the 30 early postpartum cows, eight (19 to 41 d postpartum at the time of the first AI; mean = 29.3 d) calved to the first AI and nine calved to the second synchronized estrus. The calving dates at the next calving season for these 17 cows (57% of the cows in this group) was advanced an average of 46 d (319-d calving interval). The calving rates for the two timed insemination periods were similar (P > .25) for early and later (> or = 42 d postpartum) postpartum cows. Treatment with norgestomet implants on d 12 through 21 had no detrimental effects on established or subsequent pregnancy, synchronized the return estrus of nonpregnant cows, and was efficacious in establishing pregnancy early postpartum.     

Development of a progestin-based estrus synchronization program: I. Reproductive response of cows fed melengestrol acetate for 20 days with an injection of progesterone

We designed two experiments to determine the efficacy of an estrus control system in cows that combined long-term progestin exposure (20 d) with an acute increase in progesterone concentration. In Exp. 1, cows (n = 30) were fed either melengestrol acetate (MGA; .5 mg x cow(-1) x d(-1)) or ground ear corn (MGA carrier) for 20 d. On d -15 (last day of MGA feeding = d 0), cows were administered 25 mg of PGF2alpha to regress the corpus luteum (CL) and establish an environment conducive to the development of persistent follicles. To synchronously regress persistent follicles, cows fed MGA (n = 15) were injected with 200 mg of progesterone on d -2 (MGA-P), and the cows fed the MGA carrier were not treated (CONT; n = 15). Cows in the CONT group were artificially inseminated 12 h after detection of spontaneous estrus from d -20 to d 8. Estrus was observed, and all cows in the MGA-P group were artificially inseminated during the period of estrus synchronization (SYNC; d 1 to 8). No difference in conception rate was observed between treatments. In Exp. 2, postpartum cows (n = 113) received either the MGA-P (n = 56) or CONT (n = 57) treatment. More (P < .05) cows were observed in estrus during SYNC in the MGA-P (50%) than in the CONT (28%) group. Of the cows in the MGA-P group that were not observed in estrus during SYNC, 50% were in estrus for the first time 23 to 29 d after MGA withdrawal (SYNC2), suggesting that these cows ovulated without observable estrus during SYNC. Estrus was observed for the first time during SYNC2 in more (P < .05) cows in the MGA-P (25%) than in the CONT (7%) group. Conception rate at the synchronized estrus, pregnancy rate, and interval to first service and pregnancy were similar between treatments. We conclude that administration of MGA-P results in the synchronization and(or) induction of a fertile estrus in cows.     

Effect of supplemental dietary vitamin E and zinc on reproductive performance of dairy cows and heifers fed excess iron

We tested the hypothesis that the incidence of retained fetal membranes could be reduced by limiting oxidative stress. Sixty-four primigravid heifers (56 Holstein and 8 Jersey) and 80 multiparous cows (64 Holstein and 16 Jersey) were used. A combination of vitamin E or Zn and Fe was fed in a 2 x 2 x 2 factorial arrangement during the last 42 d prepartum. Amounts of supplements per animal were 1000 IU of vitamin E (d, l alpha-tocopheryl acetate), 0.8 g of Zn (Zn-Met and ZnSO4), and 12 g of Fe (FeSO4.7H2O) for Holsteins and 9 g for Jerseys. Neither vitamin E nor Zn directly affected the incidence of retained fetal membranes, but plasma alpha-tocopherol was lower when fetal membranes were retained > 12 h or when vitamin E was not supplemented. Iron had no direct negative effects on reproductive performance, but cows receiving additional Fe had lower unsaturated iron-binding capacity, which, in turn, was also lower in cows that retained fetal membranes. Days to first observed estrus were reduced by supplementation with either vitamin E or Zn. Vitamin E reduced days to first artificial insemination (AI) and tended to reduce days open. Supplemental Zn tended to reduce days to first AI but did not affect days open. Milk production during the first 12 wk and AI per conception were not affected by supplementation with either vitamin E or Zn. Both vitamin E and Zn reduced days to first observed estrus, indicating improved reproductive health during the early postpartum period.     

Estrus detection using radiotelemetry or visual observation and tail painting for dairy cows on pasture

The efficiency and accuracy of estrus detection using HeatWatch (DDx Inc., Denver, CO) or visual observation were compared in an autumn-calving Friesian herd (n = 48 per group) and a spring-calving Jersey herd (n = 50 per group) grazing on pasture. Cows in the group monitored by the HeatWatch system were fitted with a pressure-sensitive transmitter that signaled mounting activities associated with estrus. Visual observation was carried out for about 20 min before the morning and afternoon milkings and was aided by a strip of paint applied over the tailhead. Ovarian cyclicity was monitored with progesterone concentrations in milk samples collected twice a week. The efficiency and accuracy of estrus detection were, respectively, 98.4 and 97.6% for visual observation and 91.7 and 100% for HeatWatch detection. Autumn-calving herds differed from spring-calving herds in duration of estrus (9.7 vs. 7.3 h), number of mounts (13.6 vs. 8.5), total duration of mounts (36.8 vs. 19.9 s), and mean duration of a mount (2.6 vs. 2.3 s). There was no significant variation in the distribution of the time of onset of estrus or mounting activities at different hours of the day. Conception rate was similar for AI after estrus detection with HeatWatch (65.8%) or after visual observation (65.0%). The highest conception rate was obtained when AI was carried out between 12 and 18 h after the first mount. Both the HeatWatch system and visual observation plus tail painting can be used for estrus detection of dairy cows on pasture.     

Norgestomet implants synchronize estrus and enhance fertility in beef heifers subsequent to a timed artificial insemination

Three trials involving 128 heifers were conducted to determine whether norgestomet implants administered during the mid- and late luteal phases after breeding could be used to synchronize a second estrus in nonpregnant, inseminated heifers without adversely affecting pregnancy in pregnant heifers. All heifers were initially synchronized with Syncro-Mate B and artificially inseminated 47 h after implant removal. On d 9 (Trial 1) or d 12 (Trial 2) after the timed AI, the heifers were randomly assigned to treated or control groups. Treated heifers received two silicone implants containing 10.0 mg of norgestomet each (Trial 1) or one silicone implant containing 3.6 mg of norgestomet (Trial 2). Silicone implants were removed on d 21 after the initial AI. In Trial 1, the calving rate to the initial AI of the control heifers was 35 vs 55% for the norgestomet-implanted heifers (P > .05). In Trial 2 the calving rate to the initial AI of the control heifers was 9 vs 45% in the treated heifers (P < .01). At the return estrus 52% of the control heifers returned to estrus within a 3-d period, whereas 93% of the norgestomet-treated heifers returned to estrus within a 3-d period (P < .01). Norgestomet treatment had no effect on serum progesterone concentrations of the pregnant heifers on d 21 after the initial AI. In Trial 3, both control and treated heifers were administered silicone implants containing 3.6 mg of norgestomet on d 12; additionally, the treated heifers received an injection containing 3.0 mg of norgestomet and 5.0 mg of estradiol valerate. Norgestomet implants were removed on d 21.(ABSTRACT TRUNCATED AT 250 WORDS)     

Altering conception of dairy cattle by gonadotropin-releasing hormone preceding luteolysis induced by prostaglandin F2 alpha

The objective of these experiments was to determine the effect on fertility of GnRH when used in conjunction with one or two injections of PGF2alpha. In Experiment 1, GnRH was administered 7 d before the second of two injections of PGF2alpha (14 d apart). The control group received two injections of PGF2alpha without GnRH. Conception was reduced from 63.5% for 74 controls to 48.7% for the 79 heifers and cows that had been treated with GnRH, but estrus detection and pregnancy rates were similar. In Experiment 2, 85 heifers and cows received GnRH at a random stage of the estrous cycle, followed in 7 d by PGF2alpha. Thirty to 32 h after PGF2alpha, a second dose of GnRH was given to induce ovulation of the preovulatory follicle, followed by one fixed-time insemination 18 to 19 h later (treatment designated as GnRH, PGF2alpha, and GnRH). Controls (n = 85) were given PGF2alpha and inseminated at estrus. Although conception rate was not different, one fixed-time insemination after the GnRH, PGF2alpha, and GnRH treatment tended (35.3%) to reduce fertility compared with effects of the control (47.1%). It is unclear how an injection of GnRH during the intervening week between two injections of PGF2alpha reduced fertility in Experiment 1. However, in Experiment 2, when GnRH was given 7 d before one injection of PGF2alpha and when ovulation was induced with a second GnRH injection, one fixed-time insemination seemed to produce acceptable fertility in dairy cows but probably less than that when inseminations were based on detected estrus.     

Effects of monensin on the reproduction, health, and milk production of dairy cows

A randomized clinical trial including 1109 cows from 12 Australian dairy herds was used to evaluate the effects of monensin on the health (n = > 686 cows), production (n = 915 cows), and reproduction (n = > 908 cows) of dairy cows. Cows were allocated to a treatment group receiving a slow-release intraruminal bolus containing 32 g of sodium monensin that was administered 40 d before and 50 d following the anticipated calving date or to a control group. Treatment did not significantly alter any reproductive outcome; 54.5% of cows treated with monensin and 58.2% of control cows were pregnant at first service, and days to conception were lower for cows treated with monensin. The hazard rate (0.95) was not significant for these cows. The percentage of cows pregnant was 83.8 for control cows, and days to first estrus (hazard rate = 1.04) and first service (hazard rate = 1.04) were not significantly higher for treated cows. Treatment with monensin did not significantly alter the risk of any disease. The incidence of retained fetal membranes, pyometra, lameness, abortion, and infectious diseases was not significantly lower for cows in the treatment group, and the incidence of mastitis was not significantly higher for cows in the treatment group. Monensin significantly increased milk production by 0.75 L/d per cow and tended to increase milk fat and protein yields but had no significant effect on milk fat or milk protein percentages. Changes in the production of milk and milk constituents were consistent throughout lactation.     

Fertility in estrus-cycling and noncycling virgin heifers and suckled beef cows after induced ovulation

A procedure was developed to either induce or synchronize ovulation in heifers and suckled cows. Beef females were assigned to two breeding programs: 1) two injections of prostaglandin F2alpha (PGF2alpha) given 14 d apart to synchronize estrus (PGF2alpha control; n = 179), with inseminations 12 to 16 h after detected estrus or at 80 h in the absence of estrus, or 2) two injections of PGF2alpha (d -14 and 0) plus 100 microg of GnRH on d -7 when 6 mg of norgestomet was implanted (PGF2alpha/NORG/GnRH treatment; n = 173). Implants were removed 24 h after the second PGF2alpha injection (d +1) and females were inseminated 12 to 16 h after detected estrus until 54 h after PGF2alpha. The remaining cattle were given a second 100-microg GnRH injection 54 h after PGF2alpha and inseminated 18 to 20 h later. Percentages of noncycling females with subsequently elevated progesterone (P4) on d 0 or +1 were not different between treatment groups (20.4 vs 25%), but conception rate was greater (P < .05) in noncycling treated females than in noncycling controls (55 vs 12.8%). Conception rates in cycling (59.2%) and noncycling (62.2%) treated females were similar to those in cycling controls (56.2%) but greater (P = .06) than those in noncycling controls (26.5%). Conception rates in treated females inseminated 12 to 16 h after detected estrus (63.1%) or at one fixed time (58.3%) were similar to those in controls inseminated 12 to 16 h after detected estrus (68.7%). This treatment procedure produced fertility after one timed insemination that was equal to controls inseminated after detected estrus and induced equally fertile ovulations in noncycling heifers and cows.     

Incidences and effects of diseases on the performance of Swedish dairy herds stratified by production

Incidences of diseases and their effects on reproductive performance and risk of culling in herds stratified by production and estrus detection efficiency were studied. Data were from the Swedish milk and disease recording systems and consisted of records for 33,748 first parity Swedish Friesian cows. A standardized mixed threshold model was used for statistical analyses of categorical outcome variables, and an ordinary linear mixed model was used for continuous outcome variables. An increase in production was associated with increased frequencies of treatments of most diseases, shorter intervals from calving to first artificial insemination, fewer days open, and lower culling rates. Cows treated for metritis, silent estrus, and cystic ovaries had an increased number of days to first artificial insemination and more days open. However, the negative consequences of these diseases on reproductive performance decreased as herd production increased. The risk of culling was higher for cows treated for dystocia, cystic ovaries, and mastitis, but the increase in the risk of culling was lower for higher producing herds. Similar trends were observed when herds were stratified by estrus detection efficiency. The results support the hypothesis that herd management, as characterized by milk production or estrus detection efficiency, is important in the incidences and consequences of diseases. Herd management, measured directly or indirectly, should be considered when the health status or cost of disease for a given herd is evaluated.     

Luteolysis during two stages of the estrous cycle: subsequent endocrine profiles associated with radiotelemetrically detected estrus in heifers

Our objective was to correlate hormonal changes with the timing and onset of estrus in heifers before and after luteolysis was induced with PGF2 alpha at two stages of the estrous cycle: d 6 to 9 (early; n = 10) or d 14 to 15 (late; n = 10). Blood was collected at intervals of 2 or 12 h to quantify serum concentrations of progesterone, estradiol-17 beta, and LH while heifers were observed visually for estrus and monitored for standing activity by pressure-sensitive, radiotelemetric devices. Although the concentrations of estradiol-17 beta that were associated with the putative appearance of the first dominant follicle declined before luteolysis was induced early in the cycle, some heifers that were given PGF2 alpha were in estrus as early as 35 h. Compared with heifers treated late in the estrous cycle, heifers that were treated early in the cycle produced less progesterone before PGF2 alpha treatment and had greater peak concentrations of estradiol-17 beta at estrus. In addition, heifers that were treated early in the cycle had shorter intervals from PGF2 alpha treatment to estrus, to peak estradiol-17 beta, and to peak LH and to initiation of estrus after the peak in estradiol-17 beta than did heifers treated later in the cycle. The increase in estradiol-17 beta associated with the putative first-wave follicle of the subsequent cycle and the duration of that cycle in early cycle heifers was less than after late cycle luteolysis. Results indicated that greater concentrations of estradiol-17 beta during estrus may be related to the durations of previous cycles and less progesterone exposure before luteolysis. The onset of estrus corresponded closely to, but preceded, the preovulatory LH surge by approximately 3 h.     

Effects of paced mating and intromissive stimulation on feminine sexual behavior and estrus termination in the cycling rat.

The effects of differential mating stimulation on sexual behavior and estrus length were examined in cycling rats that could or could not self-regulate, or pace, the timing of sexual contact. Female rats (Rattus norvegicus) received 30 paced, 30 nonpaced, or 15 nonpaced followed by 15 paced intromissions during mating tests. Decreases in sexual responsiveness were seen during the 2nd half of testing; pacing was associated with greater inter-intromission intervals, decreased proceptivity, and increased rejection behavior at this time. Female rats pacing during the 2nd test half behaved similarly, regardless of prior treatment, showing that the number rather than the timing of prior intromissions affected subsequent behavior. However, estrus length was decreased by prior paced mating. These data suggest that changes in sexual responsivity occur throughout estrus and that the nature of these changes is differentially dependent on the type of mating stimulation received. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of time of artificial insemination on pregnancy rates, calving rates, pregnancy loss, and gender ratio after synchronization of ovulation in lactating dairy cows

In order to assess the optimal time of artificial insemination (AI) in relation to ovulation, lactating dairy cows (n = 732) from herds with rolling herd averages of 9980 to 11,800 kg from three milkings per day were randomly assigned to five groups by stage of lactation and parity. Ovulation was synchronized by administration of GnRH followed 7 d later with PGF2 alpha followed 2 d later with a second treatment with GnRH. Cows were inseminated at 0, 8, 16, 24, or 32 h after the second injection of GnRH (ovulation occurs between 24 and 32 h after GnRH). Pregnancy diagnoses were performed by ultrasound at 25 to 35 d post-AI. Pregnancy rates per AI were similar for the groups inseminated at 0, 8, 16, and 24 h and lower for the group inseminated at 32 h. A significant quadratic effect of treatment suggests that the middle time periods (8, 16, and 24 h) may produce the greatest pregnancy rate per AI. However, the group inseminated at 0 h had lowest pregnancy loss, and the group inseminated at 32 h tended to have the greatest pregnancy loss compared with that of the other groups. The calving rate was similar between the groups inseminated at 0, 8, 16, and 24 h and lower in the group inseminated at 32 h. The time of AI also appeared to affect gender of calf: cows bred at 0 and 32 h having a higher percentage of female offspring. In conclusion, there appears to be substantial flexibility in the time of AI after the second injection of GnRH, and lower reproductive rates were observed only when AI was after the time of ovulation.     

Gonadotropin-releasing hormone enhances the calving rate of beef females administered norgestomet and alfaprostol for estrus synchronization

One hundred fifty beef heifers and 403 beef cows suckling calves were administered norgestomet implants (8 d) and alfaprostol, a PGF2 alpha analogue, approximately 28 h before implant removal. Thirty hours after implant removal, females were administered either GnRH via injection, GnRH via implantation, or no GnRH. The dosage of GnRH was 250 micrograms, and implants prolong the induced LH surge. Ovulation response, incidence of short cycles, and calving rate were analyzed as a 2 x 2 x 3 completely randomized factorial design with female (heifers and cows), estrous cycles (with or without), and GnRH as the main effects. There were no interactions (P > .10), and because heifers and cows had responses that did not differ (P > .25), they were summarized together. Females with estrous cycles had a higher (P < .05) ovulation response, fewer (P < .01) short luteal phases, and a higher (P < .01) calving rate than females without estrous cycles. Gonadotropin-releasing hormone treatment increased the ovulation response (P < .01) and the calving rate (P < .05), and these responses were not affected (P > .10) by the method of GnRH administration. Based on these data, the increased ovulation response to GnRH may account for 29% of the increase in calving rate observed in the GnRH-treated females. In summary, in norgestomet- and alfaprostol-synchronized females, GnRH enhanced calving rate regardless of how it was administered. This increase was due to more than an increased ovulation rate.     

Effect of diseases on the culling of Holstein dairy cows in New York State

The effect of seven diseases on culling was measured in 7523 Holstein cows in New York State. The cows were from 14 herds and had calved between January 1, 1994 and December 31, 1994; all cows were followed until September 30, 1995. Survival analysis was performed using the Cox proportional hazards model to incorporate time-dependent covariates for diseases. Different intervals representing stages of lactation were considered for effects of the diseases. Five models were fitted to test how milk yield and conception status modified the effect of diseases on culling. Covariates in the models included parity, calving season, and time-dependent covariates measuring diseases, milk yield of the current lactation, and conception status. Data were stratified by herd. The seven diseases and lactational risks under consideration were milk fever (0.9%), retained placenta (9.5%), displaced abomasum (5.3%), ketosis (5.0%), metritis (4.2%), ovarian cysts (10.6%), and mastitis (14.5%). Older cows were at a much higher risk of being culled. Calving season had no effect on culling. Higher milk yield was protective against culling. Once a cow had conceived again, her risk of culling dropped sharply. In all models, mastitis was an important risk factor throughout lactation. Milk fever, retained placenta, displaced abomasum, ketosis, and ovarian cysts also significantly affected culling at different stages of lactation. Metritis had no effect on culling. The magnitude of the effects of the diseases decreased, but remained important, when milk yield and conception status were included as covariates. These results indicated that diseases have an important impact on the actual decision to cull and the timing of culling. Parity, milk yield, and conception status are also important factors in culling decisions.     

Pregnancy rates for embryos transferred from early postpartum beef cows into recipients with normal estrous cycles

Survival rate of embryos from first ovulations of postpartum cows with SHORT (6.9 +/- 0.3 days; n = 35) or NORMAL (17.1 +/- 0.3 days; n = 42) luteal phases and quality of the embryos on Day 6 were compared. At 19 to 23 days postpartum, cows were allotted to receive a norgestomet implant for 9 days (normal luteal phase) or to serve as untreated controls (short luteal phase). Calves were weaned 7 days after initiation of treatment to induce behavioral estrus in cows for mating. In 25 cows, growth of the ovulatory follicle was monitored by ultrasonography. On Day 6 after estrus, embryos were recovered nonsurgically, and live embryos were transferred into recipient cows exhibiting normal estrous cycles. The medium used to flush the embryos from the uterus of each donor cow was assayed for prostaglandin F2 alpha (PGF2 alpha). Days from calf removal to estrus and size of ovulatory follicles at ovulation (4.1 +/- 0.3 days and 16.7 +/- 0.7 mm, respectively) did not differ between NORMAL and SHORT cows. Interval from detection of the ovulatory follicle to ovulation was longer in NORMAL (10 +/- 0.7 days) than in SHORT cows (8 +/- 0.6 days; p < 0.05). Rates of recovery of an embryo or ovum (64%), rates of fertilization (65%), and quality or stage of development of Day 6 embryos did not differ between SHORT and NORMAL cows. Overall pregnancy rate from recovered oocytes was 13% for SHORT and 32% for NORMAL cows (p = 0.06); survival of fertilized oocytes was 23% for SHORT and 47% for NORMAL cows (p = 0.08).(ABSTRACT TRUNCATED AT 250 WORDS)     

Relationships of body condition score to production variables in high producing Holstein dairy cattle

Practical relationships were determined between milk production, health, and reproduction with the amount and use of body fat in high producing lactating Holstein dairy cattle. Approximately 350 cows and heifers > 15 mo of age in a high producing herd were assigned body condition scores at monthly intervals for 24 mo. Production of 305-d FCM averaged 9541 kg (range 8826 to 10,818 kg). Body condition score at each of four calvings at 30, 60, 90, 120, and 305 DIM in each parity and loss in score in each lactation were summarized. Multiple regression related scores to milk and milk fat production, reproduction, and disease variables within and among lactations. No difference in score occurred at calving or at dry-off among parities. The range of body condition scores was less than is commonly reported; however, loss of condition increased with increasing parity from .3 in first lactation to .9 body condition score units in lactations > or = 4. The body condition score varied quadratically with DIM but, at a given DIM, was not related to the daily milk production on that DIM. Parity had a stronger relationship with milk and milk fat production than did body condition score. However, within lactation, body condition score at calving and the loss of score were related quadratically to milk production. No significant relationships of body condition score to the incidences of pyometra, metritis, retained placenta, cystic ovarian disease, AI per conception, days to first AI, or dystocia existed in this herd.