Hormones, metabolites, and reproduction in Holsteins, Jerseys, and their crosses

Holsteins (HH), Jerseys (JJ), and their crosses in first (n = 157) and second (n = 107) lactation were used to determine if reproduction, progesterone (P4), insulin-like growth factor 1 (IGF-1), insulin, nonesterified fatty acids (NEFA), and milk production differed between genetic groups. Thirty-four cows were Holstein-Jersey (HJ) crosses, 46 were Jersey-Holstein (JH) crosses, 48 were purebred Holsteins (HH), and 29 were purebred Jerseys (JJ) in first lactation, whereas the second-lactation animals included 23 HJ, 35 JH, 35 HH, and 14 JJ. Blood samples were collected weekly for the first 10 wk postpartum. Analyses were conducted using the MIXED, chi-square, and GLIMMIX procedures (SAS Institute Inc., Cary, NC). Seasons of calving were cold (November to May) and hot (June to October) and were combined with year to form 8 year-seasons. Days open and number of services were affected by genetic group. The HH were open 169 + 8 d, which was greater than HJ (143 + 9 d), JJ (132 + 10 d), and JH (127 + 8 d). The HH had 2.4 + 0.1 services per pregnancy, which was greater than JH (1.9 + 0.1), but not different from HJ (2.1 + 0.2) or JJ (2.1 + 0.2). Concentrations of NEFA were greater in lactation 2 (0.52 + 0.02 mEq/L) than in lactation 1 (0.45 + 0.02 mEq/L) and decreased over the 10-wk period. Concentrations of NEFA were greater in the cold season except in yr 3. Insulin in lactation 1 (0.81 + 0.03 ng/mL) was greater than in lactation 2 (0.72 + 0.03 ng/mL); insulin decreased to wk 2 then gradually increased. The HJ had the greatest insulin concentrations (0.87 + 0.04 ng/mL) and the JJ had the lowest (0.66 + 0.04 ng/mL), and IGF-1 gradually increased over the 10-wk period. Milk production (actual yield in the first 305 d, not adjusted for fat and protein) was affected by genetic group, lactation number, year-season, and wk 1 insulin. The HH produced 10,348 + 207 kg of milk, which was greater than the HJ (9,129 + 230 kg), the JH (9,384 + 190 kg), and the JJ (7,080 + 240 kg). Milk production in lactation 2 (9,676 +/- 163 kg) was greater than that in lactation 1 (8,294 +/- 160 kg). The JJ (10.3 +/- 4.7%) had the highest frequency of mastitis. The chance of getting mastitis for HH (1.1 +/- 0.9%) differed from that for HJ (9.4 +/- 4.1%), JH (8.1 +/- 3.4%), and JJ (10.3 +/- 4.7%). Genetic group affected hormones and metabolites, which may partially explain differences in reproductive measures and milk yield.