Nutrient restriction during late gestation reduces milk yield and mammary blood flow in lactating primiparous beef females

Abstract

Fall-calving primiparous beef females [body weight (BW): 451 ± 28 (SD) kg; body condition score (BCS): 5.4 ± 0.7] were individually-fed 100% (control; CON; n = 13) or 70% (nutrient restricted; NR; n = 13) of estimated metabolizable energy and metabolizable protein requirements from day 160 of gestation to calving. Post-calving, all dams were individually-fed tall fescue hay supplemented to meet estimated nutrient requirements for maintenance, growth, and lactation until day 149 of lactation. Four-hour milk yields were collected on days 21, 42, 63, 84, 105, and 147 of lactation, and milk nutrient composition was determined. Doppler ultrasonography of both pudendoepigastric arterial trunks was conducted every 21 d from day 24 to 108 of lactation. Total mammary blood flow was calculated, and hemodynamics from both sides were averaged. Data were analyzed as repeated measures with nutritional plane, day of lactation, their interaction, calving date, and calf sex (if P < 0.25) as fixed effects. We previously reported that post-calving, NR dams weighed 64 kg less and were 2.0 BCS lower than CON, but calf birth weight was not affected. Milk weight and volume were 15% less (P = 0.04) for NR dams than CON. Milk protein concentration was lower (P = 0.008) for NR dams than CON, but triglyceride and lactose concentrations were not affected (P ≥ 0.20) by nutritional plane. Milk urea N concentration of NR dams tended to be greater (P = 0.07) on day 42 but was lower (P = 0.01) on day 147 of lactation than CON. Total milk protein, triglyceride, and lactose yields were less (P ≤ 0.05) for NR dams than CON. Total milk urea N yield was less (P ≤ 0.03) for NR dams than CON on days 21, 63, and 147 of lactation. Maternal heart rate was greater (P = 0.008), but pudendoepigastric arterial trunk peak systolic velocity, resistance index, and cross-sectional area were less (P ≤ 0.04) and pulsatility index tended to be less (P = 0.06) for NR dams than CON. Mammary blood flow was 19% less (P = 0.004) for NR dams than CON, but mammary blood flow relative to milk weight or dam BW were not affected (P ≥ 0.14) by nutritional plane. Most milk yield, milk nutrient composition, and mammary blood flow variables were affected (P ≤ 0.04) by day of lactation. In summary, first-parity beef females that were nutrient restricted during late gestation and then fed to meet estimated nutrient requirements during lactation had decreased milk nutrient yield and a similar reduction in mammary blood flow.

Late gestational nutrient restriction in primiparous beef females: Performance and metabolic status of lactating dams and pre-weaning calves

“…The BCS 4 cows in Lake et al (2005) maintained body condition during early lactation, and milk production was not affected by BCS at calving. In the current study, control dams had greater milk production ( Redifer et al, 2024 ), which most likely made them more sensitive to the lipolytic demands and adipose mobilization of early lactation ( Bauman and Currie, 1980 ).…”

“…In gestational nutrient restriction models where the calves are reared naturally by their dams, it is difficult to delineate the prenatal and postnatal effects on pre-weaning growth. Given the similar reduction (15% less) in milk yield during this same period for nutrient restricted dams, which resulted in 29% less total protein, 21% less total triglycerides, 14% less total lactose, and 19% less total urea N available for their calves to consume ( Redifer et al, 2024 ), milk yield may have driven this divergence in growth. There is a strong correlation between milk yield and weaning weight ( Reynolds et al, 1978 ), explaining greater than 50% of the variation in pre-weaning ADG in 1 study ( Arthur et al, 1997 ).…”

“…Previously nutrient restricted dams gained body condition during this period, replenishing basal adipose reserves, while controls decreased body condition and backfat. Milk yield during the first 147 d of lactation was 15% less for nutrient restricted dams ( Redifer et al, 2024 ), requiring less nutrients for milk production and leaving more nutrients available for maternal tissue gain.…”

“…We reported that neonatal circulating glucose, urea N, triglycerides, and NEFA during the first 2 d of age were not affected by late gestational nutritional plane ( Wichman et al, 2023 ). Despite the large discrepancy in milk nutrients available ( Redifer et al, 2024 ), calf metabolic status pre-weaning was also minimally affected by late gestational nutritional plane. Similarly, feeding dairy calves greater amounts of milk replacer did not alter circulating glucose, urea N, triglycerides, or NEFA ( Orellana Rivas et al, 2020 ).…”

“…While being group-fed, dam BW was collected on days 168, 189, 210, and 243 of lactation (2-d BW for weaning at day 243), and jugular blood samples were collected on days 189 and 243 of lactation. Data collection during individual feeding (days 1 to 147) occurred between 1500 and 1630 h and within ± 2 d of the actual day of lactation, corresponding with 4-h milk yield collections ( Redifer et al, 2024 ). Data collection during group feeding occurred between 1200 and 1800 h (days 168 to 210) or 0700 to 1030 h (day 243) and always within ± 6 d of the actual day of lactation.…”