Effect of short-term feed restriction on temporal changes in milk components and mammary lipogenic gene expression in mid-lactation Holstein dairy cows

Abstract

Investigations of the temporal changes in mammary gene expression that occur during sudden diet change have been limited by the use of mammary tissue as the source of RNA because of the invasive nature of mammary biopsy procedures. However, the cytosolic crescent, present in 1% of the largest milk fat globules, contains mammary epithelial cell RNA that has become trapped between the inner and outer milk fat globule membranes during final formation and secretion of milk fat into the lumen of the mammary alveoli. We hypothesized that cytosolic crescent RNA extracted from milk fat could be used as an alternative source of mammary epithelial cell RNA to measure the immediate temporal changes in gene expression as a result of changes in diet. In this experiment, feed restriction was used to mimic the state of negative energy balance observed in early lactation and induce a rapid change in milk fat yield and lipogenic gene expression. Ten multiparous Holstein dairy were fed a basal diet ad libitum during a 14-d preliminary period followed by a 4-d experimental period where 5 cows remained on ad libitum feeding and 5 cows were fed at 60% of their d 8-14 intakes (restricted) on d 15 to 18 and then returned to ad libitum feeding on d 19 to 21. Milk samples were collected from each milking on d 13 to 20 and the milk fat was immediately isolated, mixed with Trizol LS, and stored at -80°C for subsequent extraction of RNA that was used for measurement of gene expression. Feed restriction tended to increase milk fat percentage. However, total milk and milk fat production were reduced by 21 and 18%, respectively. Consistent with increased use of body fat for milk synthesis, serum nonesterified fatty acids increased 6-fold (0.78 mEq/L in the feed restriction vs. 0.13 mEq/L ad libitum group), whereas the milk fatty acids <C16 decreased and ≥C16 increased by 6.5 percentage units. The lipogenic genes ACACA, FASN, and SCD1, and the transcription factor SREBF1were downregulated by 59, 36, 35, and 43%, respectively, during the feed restriction period. In addition, effects of feed restriction by day within period were detected for the genes AGPAT6, GPAM, BTN1A, and SREBF1, suggesting that temporal (day-to-day) changes in gene expression could also be detected. The results of this experiment were consistent with previous feed restriction studies in which researchers used the mammary biopsy technique to study gene expression in the mammary gland. We concluded that RNA isolated from milk fat could be used as an alternative approach to investigate rapid temporal changes in lipogenic gene expression.

Milk yield loss in response to feed restriction is associated with mammary epithelial cell exfoliation in dairy cows

“…The negative effect of feed restriction on milk production has been reported in many studies in dairy cows (Andersen et al, 2004;Radcliff et al, 2006;Guinard-Flament et al, 2007;Gross et al, 2011). As expected, feed restriction also affected the composition of milk by reducing milk protein and lactose percentages, and protein, lactose, and fat yields, as previously reported (Guinard-Flament et al, 2007;Dessauge et al, 2011;Gross et al, 2011;Abdelatty et al, 2017). Probably as a consequence of lipomobilization, the decrease in fat yield (−3.5%) was smaller than the decrease in milk yield.…”

“…Feeding level is one of the main management factors affecting milk yield and mammary gland metabolism. In lactating dairy cows, feed restriction is known to decrease milk yield (Nørgaard et al, 2005(Nørgaard et al, , 2008Guinard-Flament et al, 2007;Gross et al, 2011;Abdelatty et al, 2017). The extent of milk yield loss depends on the duration and intensity of feed restriction, as well as the lactation stage of dairy cows.…”

“…The extent of milk yield loss depends on the duration and intensity of feed restriction, as well as the lactation stage of dairy cows. A short period of severe feed restriction (cows fed 60% of their ad libitum intakes for 4 d) decreased the milk yield of mid-lactation dairy cows by 20% (Abdelatty et al, 2017), whereas a longer period of moderate feed restriction (cows fed with a control diet vs. a diet providing 80% of the energy and protein digestible in the small intestine provided by the control diet from 2 wk prepartum to 11 wk postpartum) decreased milk yield by 38% (Dessauge et al, 2011). However, there is no clear explanation of the mechanisms that lead to this decrease in milk yield induced by feed restriction.…”

Impact of post-ruminally infused macronutrients on bovine mammary gland expression of genes involved in fatty acid synthesis, energy metabolism, and protein synthesis measured in RNA isolated from milk fat

“…Cytoplasmic crescents in bovine milk are small and are present in a low proportion of milk fat globules [29]. However, the relatively high fat content of ruminant milk allows the abundance of cytoplasmic material in milk fat to be adequate for RNA isolation [33,35]. Compared with the common technique of mammary tissue biopsy, milk fat collection to obtain RNA from secretory cells for in vivo signaling analysis is noninvasive and enables a larger number of animals to be sampled at a higher frequency, and with relative ease compared to tissue biopsy.…”

Review: the cellular mechanisms underlying mammary tissue plasticity during lactation in ruminants

“…In contrast, a severe feed restriction in early lactation that reduced milk production by 38% was accompanied by decreases in LALBA and CSN3 gene expression (Dessauge et al, 2011), with no effect on CSN1S1 mRNA level. In another study, a severe feed restriction (40% less than the control diet) in mid-lactation dairy cows reduced the expression of genes involved in lipid metabolism (Abdelatty et al, 2017). Thus, the effect of feed restriction on secretory cell activity likely depends on the severity of the challenge and the timing of its application.…”