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Assessing the use of public weather station data to investigate the effects of heat stress on milk production in Canadian Holstein cattle.

I. Campos

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06-23-2020

Abstract:

153
Assessing the use of public weather station data to investigate the effects of heat stress on milk production in Canadian Holstein cattle.
I. Campos*, C. Baes, A. Canovas, F. Schenkel. University of Guelph Guelph, ON, Canada.

The objectives of this study were to identify the temperature-humidity index (THI) thresholds where heat load starts to affect production traits (milk, fat, and protein yield) in the first 3 lactations of Holstein cows, and to assess potential differences in heat stress in Quebec and Ontario. A total of 2.1 million test-day records from 167,620 Ontario cows and 3.1 million records from 225,104 Quebec cows spanning an 11-yr period (2008 — 2018) were used. The climatic data consisted of hourly measurements of ambient temperature and relative humidity. In total 58 weather stations were located within a maximum distance of 20km from each herd. A k-means cluster analysis was performed within each THI >75 to exclude herds that may have some type of cooling system. A linear model was fitted to adjust the phenotypes, which were then plotted against the THI levels for each parity. To identify the THI threshold at which milk production starts to decline, a segmented polynomial was used to describe the shape of the curve of the relationship between production and THI values. During the summer, the average THI was 69 and 68 in Ontario and Quebec, respectively. Two heat stress thresholds were identified for milk yield and protein yield, one being associated with a low decline in the yield and the other one associated with sharper decline. For both provinces, the second threshold was reached at about THI = 79 for both milk and protein yields, while the first threshold was reached at about a THI = 64 — 72 for milk yield and THI = 57 — 64 for protein yield, depending on the province and parity. The expected reduction in milk yield after a THI ~79 was −0.40 kg/d and −0.19kg/d in Ontario and Quebec, respectively. The same features for protein yield were −16.2 g/d and −9.7 g/d. For fat yield, the expected reduction in yield after a THI ~57 was −3.3g/d and −2.6g/d for Ontario and Quebec, respectively. Therefore, the estimated rate decline differed between the 2 provinces, which may be related to the higher percentage of tie stall barns in Quebec (92%) compared with Ontario (<70%).

Keywords: dairy cow, heat stress, temperature-humidity index.

Biography: Ivan Campos is currently a PhD student under the supervision of Dr Flavio Schenkel in the Centre for Genetic Improvement of Livestock (CGIL, University of Guelph). His interest in animal breeding and genetics started halfway through his Bachelor of Veterinary Medicine at the University of S�o Paulo. In 2017 he was awarded the Academic Merit Scholarship that gave him the opportunity to explore even more the world of genetics. Since then he has expanded his knowledge and developed his interests at the University of Guelph.