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Associations of mild heat stress and genetic lineage with dry matter intake, water intake, rectal temperature, and active ghrelin concentration in Holstein heifers.

C. Dechow

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06-23-2020

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Abstract:

T66
Associations of mild heat stress and genetic lineage with dry matter intake, water intake, rectal temperature, and active ghrelin concentration in Holstein heifers.
L. Han, C. Dechow*, A. Macrina. Department of Dairy and Animal Science, The Pennsylvania State University State College, PA.

The active form of the hormone ghrelin (aGHR) is involved with the regulation of feed intake, thermogenesis and energy expenditure in Holstein heifers. The objectives of this experiment were to determine 1) how ambient temperature (AT) and genetic lineage (modern genetic, MG; 1950s era sire genetics, OG) affect dry matter intake (DMI), water intake (WI), rectal temperature (RT, pre-feeding and 7h post-feeding), aGHR (pre-feeding, 1.5h post-feeding, and 7h post-feeding), and 2) associations among aGHR, DMI, and RT. Eight pregnant heifers (4 MG and 4 OG) were assigned to 7d heat treatments in a 2 � 2 Latin-square design. Each treatment group contained 4 heifers (2 MG and 2 OG). All heifers were fed once daily at 9:00 a.m. The average daily AT was 28�C for heat treatment while the average daily AT for the control environment was 22�C. Temperature-humidity-index was also considered with results nearly identical to those for AT. A repeated measures analysis of DMI, WI, RT, and aGHR was used to determine effects of genetic lineage and the covariate AT as well as associations among aGHR, DMI, and RT. The repeated effect was date with the subject heifer and significance declared at P < 0.05. Body weight (514 � 33 kg), wither height (1.47 � 0.03 m), DMI (9.9 � 0.9 kg), WI (35.3 � 4.7 L), RT (38.6 � 0.27�C), and aGHR (389 � 177 pg/mL) did not differ between MG and OG; OG had higher body condition scores than MG (4.13 vs 3.13) which indicates that MG had lower body fat percentage. AT increased RT (slope = 0.025) and WI (slope = 0.42), decreased DMI (slope = −0.09), and had no impact on aGHR (slope = 3.72, P = 0.22). aGHR 7h post-feeding had a positive association with RT pre-feeding (slope = 0.0005) and 7h post feeding (slope = 0.0003, P = 0.06). Higher DMI was associated with lower pre-feeding (slope = −0.001) and 1.5h post feeding aGHR (slope = −0.002). These results indicate that aGHR is associated with DMI and RT regulation.

Keywords: ghrelin, temperature, DMI.