-
[show abstract]
[hide abstract]
ABSTRACT: Objectives were to determine factors associated with conception rate (CR) and pregnancy loss (PL) in high producing lactating Holstein cows. In Study 1, CR was evaluated in 7633 artificial inseminations (AI) of 3161 dairy cows in two dairy farms. Pregnancy diagnosis was performed by palpation per rectum 39+/-3 days after AI. Environmental temperature was recorded at different intervals prior to and after AI. In Study 2, 1465 pregnancies from 1393 cows diagnosed at 31+/-3 days after AI by ultrasonography on three dairy farms were re-examined 14 days later to determine PL. Temperature > or =29 degrees C was considered to be heat stress (HS). Exposure to HS was defined as following: NH, no heat stress; HS1, exposure to at least 1 day of maximum temperature > or =29 degrees C and average daily maximum temperature (ADMT) <29 degrees C; and HS2, exposure to ADMT > or =29 degrees C. In Study 1, exposure of cows to HS1 and HS2 from 50 to 20 prior to AI was associated with reduced CR compared to cows not exposed to HS (28.8, 23.0, and 31.3%, respectively). Post-AI HS was not associated with CR. Cows inseminated following estrus detection or timed AI had similar CR. As the number of AI increased, CR decreased. Multiparous cows had lower CR than primiparous cows, and occurrence of milk fever and retained placenta was associated with decreased CR. In Study 2, PL was not associated with exposure to HS either prior to or after AI. Cows diagnosed with clinical mastitis experienced increased PL, but parity, number of AI, AI protocol, milk production, and days postpartum at AI were not associated with PL. In conclusion, CR was affected by HS prior to AI, parity, number of AI, and postparturient diseases, whereas PL was affected by clinical mastitis.
Animal Reproduction Science 09/2004; 84(3-4):239-55. · 1.75 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The objectives of the present study were to determine the effects of resynchronization with GnRH on Day 21 after artificial insemination (AI) on pregnancy rate and losses of pregnancy in lactating dairy cows. Holstein cows (n=585) on two dairy farms were assigned to one of two treatments in a randomized complete block design. On Day 21 after a pre-enrollment AI, animals assigned to the resynchronization (RES) group received 100 microg of GnRH i.m., whereas animals in the control (CON) group received no treatment. All animals were examined ultrasonographically on Days 21 and 28 after AI, and blood samples were taken for progesterone measurement on Day 21. Pregnancy was diagnosed on Day 28 and reconfirmed 14 days later. Nonpregnant cows on Day 28 were inseminated using timed AI after the completion of the Ovsynch protocol 10 and 17 days after enrollment in the study for RES and CON groups, respectively. Progesterone concentration > or =2.35 ng/ml was used as an indicator of pregnancy on Day 21. For RES and CON cows, pregnancy rate at Days 21 (70.9% versus 73.0%, P<0.56), 28 (33.1% versus 33.6%; P<0.80) and 42 (27.0% versus 26.8%; P<0.98) after the pre-enrollment AI did not differ. Administration of GnRH on Day 21 after AI had no effect on pregnancy loss in RES and CON groups from days 21 to 28 (53.2% versus 53.5%; P<0.94) and days 28 to 42 (17.9%; P<0.74) after AI. Pregnancy rate after the resynchronization period was similar for both treatment groups. Resynchronization with GnRH given on Day 21 after AI for initiation of a timed AI protocol prior to pregnancy diagnosis does not affect pregnancy rate and pregnancy loss in lactating dairy cows.
Theriogenology 11/2003; 60(8):1389-99. · 1.96 Impact Factor
-
Advances in Dairy Technology. 01/2003; 15.
-
[show abstract]
[hide abstract]
ABSTRACT: The dairy industry in North America has changed dramatically with a trend in direction of larger herds and higher production per cow, which seems to be associated with a decrease in fertility, especially a decrease in conception rates and extension of calving intervals (Butler, 2000; Lucy, 2001; Stevenson, 2001) . This decline in fertility of lactating dairy cows is observed not only in North America, but also in the United Kingdom (Royal et al., 2000) and Israel (Zeron et al., 2001) . Fertility measures of lactating dairy cows have reached an all time low in 1999 in the US, with services per conception of 3.0 in 143 dairy herds monitored by the Raleigh DHIA record system (Lucy, 2001) . This is similar to results reported by Overton (2002) in California with over 100,000 cows in approximately 100 dairy herds in which conception rates averaged 30.8%. The physiological and environmental stress of high producing dairy cows negatively affects estrus detection and conception. Early postpartum, lactating dairy cows undergo a period of negative energy balance (Butler, 2000; Butler and Smith, 1989). Negative energy balance results in extension of the period of postpartum anovulation. Prolonged periods of postpartum anovulation associated with negative energy balance in lactating dairy cows is inversely related to subsequent fertility (Butler, 2000). Despite the increased knowledge of the reproductive biology of the lactating dairy cow, reproductive efficiency continues to decline in dairy herds. In the high producing dairy cow, the extended period of negative energy balance, the altered competence of follicles, the lower circulating levels of estradiol during proestrus, the lower circulating levels of progesterone during diestrus, the reduced fertilization rate, and the suboptimal cross-talk between conceptus and uterus are associated with reduced fertility.
Advances in Dairy Technology. 01/2003; 15.
-
[show abstract]
[hide abstract]
ABSTRACT: The objective of this study was to examine the effects of an Aspergillus oryzae extract on milk production and composition and rumen metabolites in a commercial dairy herd. Early lactation Holstein cows, 282, in their second or greater lactation were used in a 60-day trial from August to October 2001. Cows were assigned to one of two treatments in a switchback design with two 30-day treatment periods. Treatments were control (no additive) or 5 g/day of A. oryzae extract. Both groups were fed the same total mixed ration (TMR). A. oryzae extract was blended with the TMR and fed once daily. Feeding a culture of A. oryzae had no effect on yields of milk and 3.5% fat-corrected milk. Milk components were also unaffected by A. oryzae extract, but cows fed with the control diet had higher concentration and yield of milk true protein. Rumen pH, rumen concentrations of volatile fatty acids, and NH3–N, as well as blood urea N, were similar for both treatment groups. Feeding 5 g/day of A. oryzae extract to early lactation multiparous Holstein cows had no effect on lactation performance and rumen parameters.
Livestock Production Science 86:55-59.
