No abstract

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.

No abstract

Fixed-time AI pregnancy rate following insemination with frozen-thawed or fresh-extended semen in progesterone supplemented CO-Synch protocol in beef cows SummaryThe objective of this study was to compare fixed-time AI pregnancy rate in Angus crossbred beef cows inseminated with frozen-thawed or fresh-extended semen. Two ejaculates from each of two Angus bulls were collected by artificial vagina and pooled for each bull. The pooled semen from each bull was divided into two aliquots; Aliquot 1 was extended using Caprogen ® (LIC, Hamilton, New Zealand) to a concentration of 3 × 10 6 sperm/straw and Aliquot 2 was extended using egg-yolk-glycerol extender to a concentration of 20 × 10 6 sperm/straw.Semen extended with Caprogen ® was maintained at ambient temperature and semen extended with egg-yolk-glycerol extender was frozen and maintained at GnRH im and were inseminated at a fixed-time on Day 10, 66 h after CIDR removal. Timed-AI pregnancy rates were influenced by season (P < 0.05), cows detected in estrus prior to and at AI (P < 0.001), and dam age (P < 0.01).Pregnancy rates were not affected by semen type (Fresh = 51.5% vs. Frozen = 50.4%; P = 0.66) and there were no significant interactions of semen type by estrus expression, semen type by sire, or semen type by season (P > 0.1). In conclusion, commercial beef cows inseminated with fresh-extended semen (3 × 10 6 sperm/straw) yielded comparable pregnancy rates to conventional frozenthawed semen in a progesterone supplemented, CO-Synch fixed-time AI synchronization protocol and may provide an alternative to frozen semen for more efficient utilization of superior genetics.

The presence of a developing dominant follicle may be a factor in the control of the luteolytic cascade mechanism and the number of follicular waves during the bovine oestrous cycle. In this study, ovaries of all animals were examined once a day by transrectal ultrasonography. It was expected that heifers (n = 18) would have two follicular waves if the second wave occurred later than day 10 after oestrus (Expt 1) and that cows (n = 14) would have three waves if the second wave occurred on or before day 10 (Expt 2). The objective of Expt 1 was to determine if absence of a large follicle late in the luteal phase delays luteal regression in heifers that are expected to have two follicular waves. Nine heifers were injected i.v. with 10 ml charcoal-treated bovine follicular fluid three times a day for 4 days, starting on the day after initiation of the second follicular wave, to delay growth of the second wave dominant follicle. Nine heifers were injected with 0.9% NaCl as controls. The duration of the luteal phase (calculated as the number of days that serum progesterone was > 0.5 ng ml-1) was greater (P < 0.01) in the follicular fluid-treated group compared with the controls (18.7 versus 14.1 days). FSH and follicular growth were suppressed during the period of injection of follicular fluid (P < 0.01 and 0.03, respectively). The objective of Expt 2 was to determine the effect of increased oestradiol on the duration of the luteal phase in cows that were expected to have three follicular waves. Seven cows were injected i.m. three times a day for 4 days with 1 ml oestradiol (100 micrograms ml-1 in corn oil) and seven cows were similarly injected three times a day with 1 ml 0.9% NaCl (control) starting the day after cessation of growth of the second wave dominant follicle. Luteal phase duration was shorter in oestradiol-treated animals than in the controls (14.0 versus 19.0 days; P < 0.04). Serum oestradiol concentrations were higher in the oestradiol-treated group during the period of injection (P < 0.01). In summary, luteolysis was delayed when follicular growth was suppressed with follicular fluid (Expt 1). Exogenous oestradiol administration during the development of uterine oestradiol responsiveness initiated luteolysis earlier compared with control animals (Expt 2).