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

Abstract

In dairy cows, feed restriction is known to decrease milk yield by reducing the number of mammary epithelial cells (MEC) in the udder through a shift in the MEC proliferation-apoptosis balance, by reducing the metabolic activity of MEC, or both. The exfoliation of MEC from the mammary epithelium into milk is another process that may participate in regulating the number of MEC during feed restriction. The aim of the present study was to clarify the mechanisms that underlie the milk yield loss induced by feed restriction. Nineteen Holstein dairy cows producing 40.0 ± 0.7 kg/d at 77 ± 5 d in milk were divided into a control group (n = 9) and a feed-restricted group (n = 10). Ad libitum dry matter intake (DMI) was recorded during a pre-experimental period of 2 wk. For 29 d (period 1), cows were fed either 100 (control) or 80% (feedrestricted) of their ad libitum DMI measured during the pre-experimental period. Then, all cows were fed ad libitum for 35 d (period 2). Milk production and DMI were recorded daily. Blood and milk samples were collected once during the pre-experimental period; on d 5, 9, and 27 of period 1; and on d 5, 9, and 30 of period 2. Mammary epithelial cells were purified from milk using an immunomagnetic method to determine the rate of MEC exfoliation. Mammary tissue samples were collected by biopsy at the end of each period to analyze the rates of cell proliferation and apoptosis and the expression of genes involved in synthesizing constituents of milk. Feed restriction decreased milk yield by 3 kg/d but had no effect on rates of proliferation and apoptosis in the mammary tissue or on the expression of genes involved in milk synthesis. The daily MEC exfoliation rate was 65% greater in feed-restricted cows than in control cows. These effects in feed-restricted cows were associated with reduced insulin-like growth factor-1 and cortisol plasma concentrations. When all cows returned to ad libitum feeding, no significant difference on milk yield or MEC exfoliation rate was observed between feed-restricted and control cows, but refeeding increased prolactin release during milking. These results show that the exfoliation process may play a role in regulating the number of MEC in the udders of dairy cows during feed restriction without any carryover effect on their milk production.

Phenotypic Characterization of Milk Yield and Quality Traits in a Large Population of Water Buffaloes

“…As in bovines [19,36], LC showed a gradual drop across parities but curves shapes of different parities were similar (Figure 2). In fact, again, older (multiparous) buffaloes are usually characterized by aged tissues, impaired udder epithelial integrity, greater milk SCS, lower milk LC, and poorer udder health compared to primiparous [18,[36][37][38].…”

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

“…Accordingly, a recent study showed no carryover effect of a 20% feed restriction of 4 weeks (Herve et al, 2018). This lack of persistent effect on milk yield was observed despite the negative effect of feed restriction on the number of MEC in the mammary tissue (as indicated by a higher rate of MEC exfoliation into milk; Herve et al, 2018). It is noteworthy that this was accompanied by an increase in the release of prolactin into blood at milking when cows were switched back to an ad libitum diet.…”

“…No carryover effect on milk yield has been observed regardless of the duration of the dietary challenge (from 4 days to 4 weeks; Friggens et al, 1998;Bjerre-Harpøth et al, 2012) and the stage of lactation (early, mid-or late lactation; Bjerre-Harpøth et al, 2012). Accordingly, a recent study showed no carryover effect of a 20% feed restriction of 4 weeks (Herve et al, 2018). This lack of persistent effect on milk yield was observed despite the negative effect of feed restriction on the number of MEC in the mammary tissue (as indicated by a higher rate of MEC exfoliation into milk; Herve et al, 2018).…”

“…One study showed that the reduction of milk yield with energy restriction in midlactation dairy cows was associated with a tendency for lower GT enzyme activity (Nørgaard et al, 2005). Moderate feed restriction (30% and 20% less than the control diet) increased milk protein transcripts in early lactation (Sigl et al, 2014) but did not affect them in a later stage of lactation (Boutinaud et al, 2008;Herve et al, 2018). 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.…”

“…Similarly to milking frequency, feed restriction affected the indicators of variation of cell number differently depending on the study (Table 6). Indeed, the rate of mammary cell proliferation was reported to be decreased by a restriction of the energy in the diet (Nørgaard et al, 2005) but not by a feed restriction (Dessauge et al, 2011;Herve et al, 2018). In addition, the rate of cell apoptosis was enhanced by feed restriction during early lactation (Dessauge et al, 2011) but not when applied in a later stage of lactation (Herve et al, 2018) or by energy restriction (Nørgaard et al, 2005).…”