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Enhanced pre-weaning nutrition increases mammary gland development without negatively affecting tissue composition in Holstein heifer calves
We have reported that enhanced feeding of pre-pubertal Holstein heifer calves increased mass of mammary parenchyma (PAR; 7.9x) and mammary fat pad (MFP; 5.3x). Our objective was to measure fat, protein, and DNA content of PAR and MFP in restricted and enhanced fed calves with or without estrogen. For 8 weeks, 36 Holstein heifer calves received: 1) a control milk replacer (MR) fed at 454 g powder/day (R; 20% crude protein [CP], 20% fat), or 2) an enhanced MR fed at 1135 g powder/day (E; 28% CP, 25% fat). At weaning a subset of calves were sacrificed (n = 6/diet). Remaining calves received E2 implants and were sacrificed at week 10. Treatments were: 1) R, 2) R + E2 (R-E2), 3) E, and 4) E + E2(E-E2). At sacrifice, udder haves were removed and snap frozen. Dissected MFP and PAR were analyzed for fat, protein, and DNA (Daniels et al., 2009). At weaning, E-fed calves had greater MFP protein (2.11 vs. 0.46 g; P < 0.01), DNA (22.1 vs. 4.5 mg; P < 0.01) and fat (116 vs. 3.3 g; P < 0.01). R-fed calves had increased MFP protein concentration (15.6 vs. 12.2 mg/g; P < 0.01), but MFP DNA concentration was not different. E-fed calves had increased PAR total protein (1.36 vs. 0.20 mg; P < 0.01) and DNA (20.4 vs. 2.7 mg; P < 0.01). After estrogen administration, E-E2 calves had more MFP total protein (P < 0.01), fat (P < 0.01), and greater fat concentration (P < 0.01) than all other treatments. Calves fed E-E2 had greater MFP total DNA than R and R-E2 calves (P < 0.01) but not E-fed calves. In addition, E-E2 calves had greater PAR total protein (P < 0.01) and DNA (P < 0.01) compared with all other treatments. Even further, E-E2 calves had increased total PAR fat compared with R-E2 calves (P < 0.02) and R-fed calves had decreased PAR fat content compared with all other treatments (P < 0.01). Results reinforce that composition of MFP is nutrient responsive. Moreover, data indicate that the impact of an enhanced diet on PAR tissue composition is likely positive but more research is needed to determine if observed results would correlate to altered future milk yield.
Keywords: mammary gland, milk replacer, parenchyma