title: Comparison of the impact of six heat-load management strategies on thermal responses and milk production of feed-pad and pasture fed dairy cows in a subtropical environment.
abstract: Exposure to hot environments affects milk yield (MY) and milk composition of pasture and feed-pad fed dairy cows in subtropical regions. This study was undertaken during summer to compare MY and physiology of cows exposed to six heat-load management treatments. Seventy-eight Holstein-Friesian cows were blocked by season of calving, parity, milk yield, BW, and milk protein (%) and milk fat (%) measured in 2 weeks prior to the start of the study. Within blocks, cows were randomly allocated to one of the following treatments: open-sided iron roofed day pen adjacent to dairy (CID) + sprinklers (SP); CID only; non-shaded pen adjacent to dairy + SP (NSD + SP); open-sided shade cloth roofed day pen adjacent to dairy (SCD); NSD + sprinkler (sprinkler on for 45 min at 1100 h if mean respiration rate >80 breaths per minute (NSD + WSP)); open-sided shade cloth roofed structure over feed bunk in paddock + 1 km walk to and from the dairy (SCP + WLK). Sprinklers for CID + SP and NSD + SP cycled 2 min on, 12 min off when ambient temperature >26°C. The highest milk yields were in the CID + SP and CID treatments (23.9 L cow-1day-1), intermediate for NSD + SP, SCD and SCP + WLK (22.4 L cow-1day-1), and lowest for NSD + WSP (21.3 L cow-1day-1) (P < 0.05). The highest (P < 0.05) feed intakes occurred in the CID + SP and CID treatments while intake was lowest (P < 0.05) for NSD + WSP and SCP + WLK. Weather data were collected on site at 10-min intervals, and from these, THI was calculated. Nonlinear regression modelling of MY × THI and heat-load management treatment demonstrated that cows in CID + SP showed no decline in MY out to a THI break point value of 83.2, whereas the pooled MY of the other treatments declined when THI >80.7. A combination of iron roof shade plus water sprinkling throughout the day provided the most effective control of heat load.
authors.affiliation: Meat and Livestock Australia, Sydney, Australia.
authors.forename: T M
authors.initials: TM
authors.lastname: Davison
authors.affiliation: Scottish Centre for Production Animal Health and Food Safety, Glasgow, UK.
authors.forename: N N
authors.initials: NN
authors.lastname: Jonsson
authors.affiliation: Department of Agriculture and Fisheries, Brisbane, QLD, Australia.
authors.forename: D G
authors.initials: DG
authors.lastname: Mayer
authors.affiliation: School of Agriculture and Food Sciences, The University of Queensland, Gatton, Australia. j.gaughan@uq.edu.au.
authors.forename: J B
authors.initials: JB
authors.lastname: Gaughan
authors.affiliation: Department of Agriculture and Fisheries, Brisbane, QLD, Australia.
authors.forename: W K
authors.initials: WK
authors.lastname: Ehrlich
authors.affiliation: School of Veterinary Science, The University of Queensland, Gatton, Australia.
authors.forename: M R
authors.initials: MR
authors.lastname: McGowan
mesh_terms: D000822:Animal Husbandry / Q000379:methods*; D000818:Animals; D001831:Body Temperature; D002417:Cattle; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects*; D006799:Housing, Animal; D006813:Humidity; D008892:Milk; D011247:Pregnancy; D056152:Respiratory Rate; D014329:Tropical Climate
keywords: Cooling strategies; Dairy production; Heat-load; Subtropical