Effect of heat-stress on conception in a dairy-herd model in the Natal highlands of South Africa

Regression models are proposed for predicting conception rate in a dairy herd under South African and especially Natal conditions. Conception rate (CR%) was related to mean monthly temperature-humidity index (THI) by curvilinear regression equation model; CR% = -812,7 + 28,61THI - 0,2322THI² (P = 0,061), and by linear regression equation model; CR% = 188,0 - 1,906THI (P = 0,023). Conception rate was related to numerical month of the year (M) by: CR% = 44,34 + 6,168M - 0,428M² (P = 0,1 06). Further investigations to test the proposed regression models under various dairy-herd conditions and to improve reproduction in South African dairy herds are needed.The articles have been scanned in colour with a HP Scanjet 5590; 600dpi. Adobe Acrobat XI Pro was used to OCR the text and also for the merging and conversion to the final presentation PDF-format.mn201