Fertility of Lactating Dairy Cows Administered Recombinant Bovine Somatotropin During Heat Stress

Abstract

Administration of recombinant bovine somatotropin (bST) to lactating dairy cows during heat stress increases milk yield, but it also can increase body temperature and may therefore compromise fertility. However, it is possible that bST treatment could increase fertility during heat stress because it has been reported to increase fertility in lactating cows. In addition, bST increases secretion of insulin-like growth factor-I (IGF-I) that promotes embryo survival. The purpose of this study was to determine effects of bST on reproductive function in lactating dairy cows during heat stress. The experiment was conducted in southern Georgia from July to November 2005 using lactating Holstein cows (n = 276 for reproductive traits). For first service timed artificial insemination (TAI), cows were presynchronized with 2 injections of PGF(2alpha) given 14 d apart followed by a modified Ovsynch protocol (GnRH and insemination at 72 h following PGF(2alpha) ). Pregnancy was diagnosed by using ultrasonography on d 29 and reconfirmed by palpation between d 45 and 80 post-TAI. Nonpregnant cows were resynchronized with the modified Ovsynch protocol and received a second TAI. Treatment with bST started 1 wk before the start of Ovsynch and continued at 2-wk intervals. Blood samples were collected from a subset of cows to determine IGF-I profiles immediately before the first bST injection, 1 wk later, and at d 35 of bST treatment. Rectal temperatures were assessed on d 29 of bST treatment. Pregnancy rates (d 45 to 80 post-TAI) did not differ between bST and control cows for first- (16.7 vs. 15.2%) or second-service TAI (14.8 vs. 17.2%). Plasma concentrations of IGF-I and milk yield were greater for bST-treated cows following the initiation of bST treatment and bST increased rectal and vaginal temperatures. Body condition score was less for bST-treated cows. In conclusion, treatment with bST during heat stress increased IGF-I concentrations, milk yield over time, and rectal and vaginal temperatures without affecting first- or second-service pregnancy rates. Thus, at least under certain housing conditions, bST can be used to improve milk yield during heat stress without compromising fertility.

Two 250 mg Doses of Bovine Somatotropin Increase Conception Rate, IGF-I Plasma Concentration and Reduce the Days to Estrus in Holstein Cows Following Estrus Synchronization

“…1, 2). Our results are consistent with those of Lucy (2000) and Jousan et al (2007). Therefore, it is possible that the same effect also happens in uiuo, because I G F -I concentration of follicular liquid rises after bST administration.…”

“…1GF-I acts as a factor of embryonic s u r v i v a l , since i t diminishes the damage caused by embryotoxic factors (Jousan a n d H a n s e n , 2004). The treatment with 500 mg bST around the 60th day postpartum possibly has a negative effect on conception rate, since it causes a n increase in milk production (Bilby et d , 2006) and a n increment in body temperature (Jousan et al, 2007). Consequently cows suffer from a severe negative energy balance, which normally happens during the first 60 d postpartum.…”

Development of a self-contained, indwelling vaginal temperature probe for use in cattle research

“…Other researchers have utilized similar devices for measuring vaginal temperature (Suthar et al, 2011;Dikmen et al, 2009;Jousan et al, 2009;Kendall et al, 2009;Vickers et al, 2010;Zimbelman et al, 2010;Nabenishi et al, 2011); however all of the aforementioned studies were conducted in dairy cows, not beef heifers as in the current study. Other studies have used larger vaginal temperature devices (Hillman et al, 2009;AlZahal et al, 2011), which may not be appropriate for smaller beef cows and heifers.…”

Heat stress and ACTH administration on cortisol and insulin-like growth factor I (IGF-I) levels in lactating Holstein cows

“…Similar results were previously described (McGuire et al 1991;Hirayama et al 2004;Chaiyabutr et al 2008). Other authors, in opposition to the aforesaid, reported that bovine somatotropin treatment, under heat stress, increased milk production, IGF-I release and RT in dairy cows (Sarko et al 1994;Jousan et al 2007).…”