Effects of nutrient intake level on mammary parenchyma growth and gene expression in crossbred (Holstein × Gyr) prepubertal heifers

Abstract

This study investigated the effects of increased nutrient intake levels on prepubertal mammary parenchyma development in crossbreed (Holstein × Gyr) dairy heifers. Eighteen heifers age 3 to 4 mo were fed 1 of 3 nutrient intake levels (n=6 per treatment) designed to sustain an average daily gain of 0.0kg/d (maintenance, MA), 0.5kg/d (low gain, LG), or 1.0kg/d (high gain, HG). Serum blood samples collected on d 42 and 84 after a 12-h fast were analyzed for triglycerides, leptin, insulin, and insulin-like growth factor 1 (IGF-1). Liver and mammary parenchyma were biopsied on d 42 and harvested on d 84 for gene expression analysis. Parenchyma samples were also used for biochemical and histological analysis. Mammary parenchyma weight was lower in HG than in MA or LG heifers, but mammary extraparenchymal fat was greater in HG heifers than in other groups. Heifers fed the HG diet had a greater fraction of ether extract in their parenchyma than the others and a smaller fraction of crude protein in their parenchyma than MA heifers. Moreover, the HG and LG heifers had greater body fat mass than MA heifers. Nutrient intake level had no effect on the number of intraparenchymal adipocytes. Heifers fed the HG diet had greater serum IGF-1 than the others, and serum insulin was lower in the MA than the HG or LG heifers. Liver GHR, IGF1, and IGFBP3 mRNA expression was higher, but IGFBP2 mRNA was lower in HG heifers than in others. The parenchyma mRNA expression of lipogenic markers, such as CD36, ACCA, FASN, and ADIPOR1, was upregulated by nutrient intake level. Significant nutrient intake × time interactions for lipogenic genes during the experimental period indicated variable gene expression depending on the time point of prepubertal mammary gland development. Overall, our data suggest that enhancing nutrient intake increased body fat accumulation and lipogenesis in the mammary gland to the detriment of parenchyma growth. Moreover, increased lipogenesis in the parenchyma of HG heifers may indicate that fat accumulation occurred because of adipocyte hypertrophy and not differences in adipogenesis. The implications of these results for milk yield needs to be elucidated.

Technical note: Mammary gland ultrasonography to evaluate mammary parenchymal composition in prepubertal heifers

“…Eighteen crossbred heifers Holstein:Gyr were used in this experiment; they were part of a larger experiment that dealt with effects of nutrient intake on mammary growth and composition. Full experimental details are reported elsewhere (Weller et al, 2016). Briefly, heifers were allotted to 1 of 3 dietary treatments when they were 3 to 4 mo of age (BW, 102.2 ± 3.4 kg).…”

“…At the end of the 84-d experiment, heifers were slaughtered (140.0 ± 8.0 kg and 200 d old) to assess body and mammary composition (Weller et al, 2016). Relevant dependent variables reported by Weller et al (2016) and also used here include number of adipocytes in PAR (Nad), epithelial area (Ep), percent crude protein of PAR (%CP), percent ether extract of PAR (%EE), PAR weight (WPAR), and mammary fat pad weight (WFAT) in these same heifers. For full description of methodology on these 6 dependent variables, the reader is directed to Weller et al (2016).…”

Metabolic and hormone profiles of Holstein x Gyr cows during pre- and postpartum

“…In this context, the Holstein x Zebu cross emerged as an alternative to reduce impacts on dairy production and cow reproduction in several regions of Brazil, since Zebu animals are well adapted to tropical conditions (Santana Jr. et al, 2015). Among the Zebu breeds, Gyr is particularly well adapted to Brazilian environmental conditions and it has been intensely used in dairy crossbreeding, being the preferred breed for this purpose in the country (Pereira et al, 2012;Weller et al, 2016).…”

Post-weaning feeding levels on feeding behavior, growth and development in Holstein dairy heifers

“…However, when highenergy diets are used in an attempt to achieve high weight gains before puberty, there is an excessive fat deposition that could adversely affect the mammary gland development (SILVA et al, 2002). For example, WELLER et al (2016) reported that 3-month old heifers fed to achieve an average daily weight gain (ADWG) of 1.0kg had a higher mammary fat pad mass and a lower mammary parenchyma mass than heifers with an ADG of 0.5kg.…”