Fig. 4.1
(a) Mean (±SD) plasma concentrations of NEFA (μEq/L) in cows subjected to different dry period lengths. (b) Mean (±SD) plasma concentrations of IGF-I (ng/mL) in cows subjected to different dry period lengths. (A,B P ≤ 0.01)
The IGF-I in group T declined to a nadir of 8.2 ng/mL in the first week PP, and then showed a positive trend until the end of the study (100.7 ng/mL). On the contrary, subjects in group C showed a decline in IGF-I levels from 58.9 to 9 ng/mL in the last weeks of pregnancy, and, after parturition, IGF-I returned to the initial levels (56.8 ng/mL) (Fig. 4.3b). The shortening of the dry period significantly raised the content of IGF-I in the final stages of the dry period and during early lactation (P ≤ 0.01).
The resumption of ovarian activity, based on changes in milk whey P4, was recorded in 10 of 13 cows with short dry periods and 9 of 12 cows with traditional dry periods. Subjects in group T showed a significant decrease of the time interval required for the resumption of ovarian activity as compared to cows in group C (34.5 ± 3.55 vs. 46.9 ± 2.3 days, P ≤ 0.01).
4.4 Discussion
The reduction of the dry period to 5 weeks resulted in significant differences in the resumption of ovarian activity within 14 weeks PP in terms of time (34.5 vs. 46.9 days), but not numerically (76.9 vs. 75.0%). These results partially differ from data reported by Watters et al. (2009), who recorded, after a dry period of 34 days, a shorter interval between calving and first ovulation (35 vs. 43 days) and also a higher ovulation rate at 70 days of lactation (92 vs. 82%).
The pattern of NEFA plasma concentrations did not change significantly between the two treatment groups, which is in contrast to what was reported by de Feu et al. (2009). The levels of IGF-I observed in group T were instead significantly higher during both the last part of the dry period and the first 14 weeks of lactation, displaying an improved energy balance as compared to the traditional dry period group.
Whole-milk production underwent a reduction of 4%, much lower than the 19% reported by de Feu et al. (2009), during the first 12 weeks of lactation. However, milk quality in terms of fat and protein content was not affected by the length of the dry period.
In conclusion, a reduction in the dry period resulted in a decrease in milk production, but improved the periparturient endocrine status, with a positive impact on both the metabolic balance and the time of postpartum resumption of ovarian activity.
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