1824
Effects of a Corn Straw or Mixed Forage Diet on mammary gland function and its endocrine regulation in early lactation dairy cows
The forage system is critical to lactation performance in dairy cows. The objective of this study was to evaluate the effects of two different forage patterns on the mammary gland and the endocrine regulation of its functions. Twelve multiparous, early-lactation Holstein cows were randomly assigned to high forage diet (MF, forage: concentrate = 60 : 40) with Chinese wildrye, alfalfa hay and corn silage as the forage source or low forage diet (CS, forage : concentrate = 40 : 60) with corn straw as the forage source. Body weight (BW), body condition score (BCS) and dry matter intake (DMI) of each cow were recorded. Milk yield were recorded daily，and milk compositions and somatic cell count (SCC) were detected. Blood samples were collected weekly, and mammary biopsies were taken on 16 days postpartum. Data were analyzed using the PROC MIXED procedure of SAS 9.1. From the 6-wk of lactation, cows fed MF diet produced more milk (23.05 and 18.24 kg/d; P < 0.05), and tended to produce more milk fat (1.08 and 0.81kg/d; P = 0.07) and protein (0.69 and 0.59kg/d; P = 0.10) compared with cows fed CS diet. In CS group, the milk SCC were greater than those in MF group (Somatic cell score: -5.25 and -6.88; P = 0.02). There were no differences in BW, BCS and DMI (P＞0.05). Compared to MF cows, insulin like growth factor-I (IGF-1) in blood (70.21 and 50.49 ng/mL; P < 0.05) and IGF-1R expression in mammary (1.86 ± 0.15 and 1.45 ± 0.11; P = 0.02) were lesser in CS group. Mean concentrations of serum BHBA (1.64 vs 0.51 mmol/L; P < 0.0001) and NEFA (832.3 vs 309.0 μEq/L; P ＜0.01) in MF cows peaked in week 2 after calving, and greater than CS group. The secretory activity of mammary epithelial cells (MEC) and the rate of mammary cell proliferation in both groups had no significant difference (P > 0.05)，but the rate of cell apoptosis in CS group were greater relative to the MF group (1429 ± 103 and 679 ± 128 counts/mm2; P = 0.003). The results indicated that lactation performance of dairy cows were affected by forage patterns, which was closely related to their endocrine regulation in dairy cows.
Keywords: forage sources,mammary gland function,endocrine regulation