Effect of Lactation Yield on First Follicular Wave Surge After Calving of Crossbred Dairy Cattle

Abstract: This study aimed  to evaluate the effect of lactation on first follicular wave surge of crossbred (Gir x Holstein) dairy cattle.  Nine multiparous crossbred dairy cattle were divided according to daily milk production (Group 1 = milk production higher than average, n = 5; Group 2 = milk  production  lower  than  average,  n  =  4).  From  calving  (Day  0)  until  divergence  of  first follicular wave, ovaries  was monitored daily by ultrasound exams to observed the follicular emergence,  growth  rate,  maximum  follicular  diameter,  day  of  follicular  divergence  and ovulation. The mean of milk production was 17.4 + 6.4 L/day (n= 9). Group 1 had higher daily milk production than Group 2 (21.8 + 3.8 L/day vs. 11.9 + 3.9 L/day, P 0.05). The growth  rate of first follicular surge was higher  in  Group  2  than  Group  1  (2.0 + 0.0  mm/day  vs  1.2 + 0.6  mm/day,  P<  0.05).  The maximum follicular diameter was 11.6 + 0.9 mm (Group 1) and 13.5 + 1.7 mm (Group 2); P< 0.05. The follicular divergence occurred earlier  in Group 1 than Group 2 (12.2 + 0.8 days vs 13.7 + 0.6 days; P< 0.05). One animal of Group 2 ovulated. In conclusion, data suggested that milk production had influence on ovarian follicular dynamic after calving. Keywords : Follicle, post-partum, lactation, dairy cattle


Introduction
Several researchers had studied the effect of lactation on fertility of cattle (Butler et al., 2006;Cavalieri et al., 2006). Many factors have negative effect on follicular surge in early post-partum of dairy cattle.
Ovarian recrudescence with normal re-occurring estrous cycles and restoration of fertility to first service are associated with a reduced occurrence of periparturient metabolic and reproductive disorders. Marked negative changes in energy balance and reduced immunocompetence influence gonadotropic and metabolic hormones (Thatcher et al., 2006).
After parturition, dairy cows experience a rapid increase in milk yield, and increased mobilization of body adipose tissue (Lederman, 2004). It is normal for dairy cows to undergo a process of adipose tissue mobilization in early lactation because energy demand for milk production is greater than the energy provided by the diet (Koltes et al., 2011). The severity and duration of the negative energy balance may be influenced by genetic merit for milk yield (Gross et al., 2011). The reproductive performance of cattles, particularly the probability of conception, may be negatively associated with the magnitude and duration of negative energy balance in early lactation (Walsh et al., 2011) In addition, much of the effort has focused on the nature of the signal (endocrine or otherwise) that controls pituitary secretion of LH and FSH, the response of the ovary to LH and FSH (Lucy, 2003). Plasma FSH levels rise in most cows 5-10 days after calving and thereafter the random changes observed have little relationship to the onset of cycles. Recovery of FSH release therefore is earlier post partum than recovery of LH release. Plasma LH concentrations undergo significant changes directly related to the initiation of ovarian cycles, with low plasma levels immediately post-partum, followed by an increase in basal secretion and the development of clear LH episodes. (Jorritsma et al., 2005) There is much information about physiologic patterns during early postpartum period. However, there are few publications about the lactation effect on follicular surge in crossbred dairy cattle at field condition. Thus, the aim of this study was to evaluate the effect of milk production on first follicular wave surge of crossbred (Gir x Holstein) dairy cattle.

Animals and groups
Nine multiparous crossbred dairy cattle (½ Gir x ½ Holstein) with body condition score (BCS) = 3.0 (scale 1 to 5; very fin = 1 and very fat = 5) were divided in two groups according to daily milk production (Group 1 = milk production higher than average, n = 5; Group 2 = milk production lower than average, n = 4). All animals were maintained in pasture regimen with mineral salt support and milked twice/day (at 7h00min and 16h00min).

Follicular evaluation
From calving (Day 0), the ovaries was evaluated daily by ultrasound exams (Pie Medical 480, Maastricht, Netherlands) with a rectal 5 MHz probe. All exams were performed after morning milk. Data of follicular emergence, growth rate, maximum diameter, moment of divergence and ovulation were recorded and analyzed according to milk production of animals.

Statistical analysis
The ANOVA was used to evaluate the continuous variables (follicular emergence, growth rate, maximum diameter, moment of divergence or atresia and ovulation) for repeated measure. The T-test was used to evaluate the differences between means.

Results and Discussion
The mean of daily milk production was 17.4 + 6.4 L/day (n = 9). Animals of Group 1 had higher daily milk production than Group 2 (21.8 + 3.8 L/day vs. 11.9 + 3.9 L/day, P < 0.001). Data of follicular emergence was similar in both groups (P > 0.05). The growth rate of first follicular surge was higher in Group 2 than Group 1 (2.0 + 0.0 mm/day vs. 1.2 + 0.6 mm/day, P < 0.05). The maximum follicular diameter observed was 11.6 + 0.9 mm (Group 1) and 13.5 + 1.7 mm (Group 2); P < 0.05. The follicular divergence occurred earlier in Group 1 than Group 2 (12.2 + 0.8 days vs. 13.7 + 0.6 days; P < 0.05). Only one animal (25%) of Group 2 presented ovulation. Gutierrez et al. (2006) reported that the first ovulation and commencement of normal luteal function occurred significantly earlier in low (L) line cows than high (H) line cows. The average daily milk production during the study period did not differ (P>0.10) between cows in either the H (= 31.0+/-1.5kg/day) or L (= 30.2+/-1.7kg/day) PBV lines although, 305 days milk production was significantly different (P < 0.01; H = 6880 +164kg versus L = 5795 + 317kg). In both studies the first ovulation postpartum occurred earlier (P<0.01) in the L (day 19) versus the H line (day 28). At day 15 postpartum all cows had follicles of all three-size categories (small, medium-sized and large). Small (P<0.07) and mediumsized follicle numbers increased (P<0.01) with day postpartum. However, the inclusion of predicted changes in body weight as a covariate in the analysis, demonstrated that changes in number of small and medium-sized follicles were associated with changes in body weight.
The numbers of cows showing ovulation and anovulation within 3 weeks postpartum were 31 (70.5%) and 13 (29.5%) in the primiparous cows and 35 (53.0%) and 31 (47.0%) in the multiparous cows, respectively. The patterns of ovarian resumption after calving were classified into two types (normal ovarian cycles and abnormal ovarian cycles) on the basis of milk P4 concentrations. Initiation of normal ovarian function in cows ovulated within 3 weeks postpartum occurred earlier than in anovulation cows regardless of the number of calvings (primiparous, 27.8 days vs. 44.4 days; multiparous, 30.6 days vs. 55.7 days; P<0.01). (Kawashima et al., 2006) In cattle, treatment with recombinant bovine somatotrophin (rGH) significantly increases the population of small ovarian follicles. This is associated with increases in circulating concentrations of insulin and insulin-like growth factor-I (IGF-I). Subsequent studies, both in vitro and in vivo, have highlighted the importance of IGF-I and/or insulin acting in synergy with FSH and LH. More recently, we demonstrated that feeding heifers with 200% maintenance requirements for a short period significantly increases circulating insulin concentrations and population of small ovarian follicles. (Gong, 2002) Increasing the suckling intensity further delayed the onset of ovarian cyclicity, probably by increasing the frequency or strength of its inhibitory influence on hypothalamic activity. Plasma FSH levels rise in most cows 5-10 days after calving and thereafter the random changes observed have little relationship to the onset of cycles. Recovery of FSH release therefore occurs earlier post partum than recovery of LH release. Hyperprolactinaemia is not a cause of reproductive failure in milked or suckling cows because there is no correlation between plasma prolactin levels and the onset of ovarian cycles. Plasma LH concentrations suffer significant changes directly related to the initiation of ovarian cycles, with low plasma levels immediately post partum, followed by an increase in basal secretion and the development of clear LH episodes. This pulsate pattern appears earlier in dairy than in beef cows and is further delayed by suckling compared to milking. Before the first ovulation there is an increased frequency and peak height of LH episodes leading to a rise in plasma LH levels and eventually to a preovulatory LH surge which results in the first ovulation. These changes in the pattern of LH release appear definitive in the initiation of ovarian activity in post-partum cows. (Crowe, 2008).

Conclusion
Data of this experiment suggested that daily milk production had influence on