Effect of eCG on early resumption of ovarian activity in postpartum dairy cows
Introduction
The resumption of normal ovarian activity after parturition is one of the major concerns for regaining breeding potential in dairy cows. In high-producing Holstein herds, 6–59% of the postpartum cows have not resumed cyclicity by Day 60 postpartum (Cerri et al., 2004, Santos et al., 2009, Stevenson et al., 2006). A new follicular wave commenced about 5–7 days after parturition (Beam and Butler, 1997, Beam and Butler, 1998) and the newly emerged follicle may reach to the large size by Day 10 postpartum (Savio et al., 1990a). Regardless, great variation exists in the fate of the first recruited dominant follicle; 46% ovulated and 23% became cystic (Beam and Butler, 1999). Ovulation of the first wave dominant follicle could decrease postpartum anoestrous by 31 days (Beam and Butler, 1999). The proportion of anestrus was greater in primiparous than multiparous cows in the first 60–70 days postpartum (Cerri et al., 2004, Moreira et al., 2001). Primiparous cows were 52% less likely to have initiated estrous cycles by 65 days postpartum than multiparous cows (Santos et al., 2009). It is well documented that cows with early resumption of ovarian function have higher fertility (Galvão et al., 2010, Kinsel and Etherington, 1998, Senatore et al., 1996, Stevenson and Call, 1983, Thatcher and Wilcox, 1973). Minimizing the interval from calving to the first ovulation provides ample time for completion of multiple ovarian cycles (more luteal phases) prior to insemination, which in turn improves conception rate (Butler and Smith, 1989)
Equine chorionic gonadotropin (eCG) has both FSH and LH like activity and parenteral administration stimulates follicular growth and ovulation in cattle (Gonzalez-Menico et al., 1978, Newcomb et al., 1979). There is a marked inter-dependence of activity between the ovaries and the uterus shortly after parturition. The early resumption of ovarian activity leading to the availability of circulating oestradiol-17β may help to hasten uterine involution through a reduction in size, a marked increase in uterine tone (Hussain, 1989) and benefits to the uterine defense mechanisms (Rowson et al., 1953). Equine chorionic gonadotropin administrated on Day 14 postpartum increased follicular growth in the ovary ipsilateral to the previously gravid uterine horn, and increased plasma oestradiol concentrations, but did not affect uterine involution and subsequent reproductive performance (Sheldon and Dubson, 2000). Equine chorionic gonadotropin was also used to enhance follicle growth at the conclusion of estrous synchronization programs in beef cows to stimulate follicular growth, ovulation rate and plasma progesterone concentrations during the ensuing cycle (Cutaia et al., 2003).
The working hypothesis of this study was that the injection of eCG, concurrent with the emergence of the first wave ovarian follicle, on Day 6 postpartum may enhance ovarian follicle development leading to spontaneous ovulation or induced ovulation by hCG. This in turn may provide sufficient time for multiple estrous cycles prior to the first service in lactating primiparous Holstein cows.
Section snippets
Experimental location
This experiment was conducted at the experimental dairy herd of the Veterinary Research Institute, Faculty of Veterinary Medicine, University of Tehran (latitude: 35°39′8″N; longitude: 51°26′38″E; altitude: 1029 m).
Animals and experimental design
Healthy primiparous Holstein cows calved between November 2009 and June 2010, without puerperium disorders, such as retained placenta and dystocia were selected. Cows with any digestive and/or reproductive disorders such as clinical endometritis, clinical mastitis, lameness, and
Results
Based on the thrice daily milking information, the average daily milk production (from the start of milking to 60 days post-calving) in control, eCG and eCG–hCG groups were 22.6 ± 0.84, 22.1 ± 1.30, and 22.0 ± 1.05 kg/day, respectively (P > 0.05).
Discussion
The main purpose of this study was to enhance the first wave ovarian follicle development by injecting eCG on Day 6 postpartum in primiparous Holstein cows. This strategy was further complemented by incorporating hCG to induce ovulation of the first wave dominant follicle following eCG treatment aiming at the establishment of the estrous cycle with normal length after the first ovulation postpartum. Hypothetically, this in turn, allows the dairy cow to resume normal and multiple estrous cycles
Acknowledgements
Research was funded by the Research Deputy of the University of Tehran and Center of Excellence for Veterinary Research on Iranian Indigenous Animals. The authors wish to express their great appreciation to Dr Zahra Rezaei Ghahroudi, from Statistical Research Institute, Iranian Statistical Center, for her valuable comments on analyzing non-parametric data.
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