ABSTRACT

The stress of the early postpartum period can be exacerbated by heat stress for those cows calving in late summer with potential negative effects on postpartum recovery. The objective of this research was to determine if early postpartum treatment with gonadotropin-releasing hormone and prostaglandin F2 would speed postpartum recovery in lactating Holsteins calving in late summer. Thirty-four Holsteins calving during August, either were injected with gonadotropin-releasing hormone 13 to 15 d postpartum followed by prostaglandin F2 12 d later or maintained as control with no injections. Between 13 to 15 d and 44 to 46 d postpartum, all were observed for estrus twice daily using androgenized heifers. Blood samples were drawn twice weekly for determination of progesterone concentrations. On d 25, 36 and 45, uteri were palpated to assess degree of involution and ovaries were scanned ultrasonically to determine size and number of antral follicles as well as presence and size of corpora lutea. Average daytime rectal temperatures were 39.9^o C for both treated and control cows. Days to first observations of estrus were 27.0 and 36.1 for treated and control cows, respectively (P<0.05). Progesterone concentrations were higher in treated cows than controls between d 37 to 45 postpartum (P<.05), but did not differ for d 15 to 25 or d 26 to 36. More treated cows had observable corpora lutea on d 36 and 45 than did controls (P<.05). Treated cows had more complete uterine involution (P<.01) on d 36 and 45 but were not different from controls on d 25. Therefore, early postpartum treatment of cows with gonadotropin-releasing hormone followed by prostaglandin F2 resulted in more rapid postpartum recovery as indicated by expression of estrus, observable corpora lutea, and uterine involution, thus providing potential for higher fertility.

¹College of Veterinary Medicine, Mississippi State University