Postabsorptive carbohydrate adaptations to heat stress and monensin supplementation in lactating Holstein cows

Abstract

Multiparous cows (n=34, 89 d in milk, 537 kg) housed in environmental chambers were fed a control total mixed ration or one containing monensin (450 mg/cow per day) during 2 experimental periods (P): (1) thermal neutral (TN) conditions (constant 20°C) with ad libitum intake for 9 d, and (2) heat stress (HS, n=16) or pair-fed [PF; in TN (PFTN); n=18] for 9 d. Heat-stress was cyclical with temperatures ranging from 29.4 to 38.9°C. Rectal temperatures and respiration rates increased in HS compared with PFTN cows (38.4 to 40.4°C, 40 to 93 breaths/min). Heat stress reduced dry matter intake (DMI, 28%), and by design, PFTN cows had similar intakes. Monensin-fed cows consumed less DMI (1.59 kg/d) independent of environment. Milk yield decreased 29% (9.1 kg) in HS and 15% (4.5 kg) in PFTN cows, indicating that reduced DMI accounted for only 50% of the decreased milk yield during HS. Monensin had no effect on milk yield in either environment. Both HS and PFTN cows entered into calculated negative energy balance (-2.7 Mcal/d), and feeding monensin increased feed efficiency (7%) regardless of environment. The glucose response to an epinephrine (EPI) challenge increased (27%) during P2 for both HS and PFTN cows, whereas the nonesterified fatty acid response to the EPI challenge was larger (56%) during P2 in the PFTN compared with the HS cows. Compared with P1, whole-body glucose rate of appearance (Ra) decreased similarly during P2 in both HS and PFTN cows (646 vs. 514 mmol/h). Although having similar rates of glucose Ra, HS cows synthesized approximately 225 g less milk lactose; therefore, on a milk yield basis, glucose Ra decreased (3.3%) in PFTN but increased (5.6%) in HS cows. Regardless of environment, monensin-fed cows had increased (10%) glucose Ra per unit of DMI. From the results we suggest that the liver remains sensitive but adipose tissue becomes refractory to catabolic signals and that glucose Ra (presumably of hepatic origin) is preferentially utilized for processes other than milk synthesis during HS.

A supplement containing multiple types of gluconeogenic substrates alters intake but not productivity of heat-stressed Afshari lambs1

“…This observation agrees with our previous sheep study (Mahjoubi et al, 2014) and other ovine reports (Sano et al, 1983;Sevi et al, 2001;Caroprese et al, 2012;Alhidary et al, 2012). Furthermore, the increased NEFA concentration in PFTN controls compared with HS animals replicates findings across species, as similar results have been reported in pigs (Pearce et al, 2013;Sanz Fernandez et al, 2015), steers (O'Brien et al, 2010), and lactating cattle (Wheelock et al, 2010;Baumgard et al, 2011). It is of interest to determine how much the increased adipose mobilization in the PFTN controls contributed to the decreased ADG compared with the HS lambs.…”

Effects of a supplement containing multiple types of gluconeogenic precursors on production and metabolism in Holstein bull calves during heat stress

“…Consequently, safely providing rumen substrates that are gluconeogenic themselves (glycerol; if absorbed intact by the intestine or rumen wall) or are metabolized into glucose precursors (propionate) may increase productivity during the warm summer months (Baumgard and Rhoads, 2012). Dietary ionophores safely increase propionate production and can increase hepatic glucose output (Baumgard et al, 2011). Another dietary option to increase propionate production is via supplementing glucose precursors, such as glycerol and propylene glycol, which have been used for prophylactic and metaphylactic treatment for ketosis (Johnson, 1954;Fisher et al, 1973).…”

Field Trial on Glucose-Induced Insulin Response in High-Yielding Dairy Cows under Different Environmental Temperatures

“…Generally, cows exposed to heat stress during the summer season appeared to have a higher insulin response following an intravenous glucose load as compared with their spring counterparts. [15] midlactation heat-stressed cows appear to have a preference to use glucose as an oxidative substrate. The resulting increase in insulin response shifts glucose into other peripheral tissues at the expense of the mammary gland.…”