EFFECT OF DRAFT WORK ON PERFORMANCE AND METABOLISM OF CROSSBRED COWS .1. EFFECT OF WORK AND DIET ON BODY-WEIGHT CHANGE, BODY CONDITION, LACTATION AND PRODUCTIVITY

Forty pregnant F-1 crossbred dairy cows (20 Friesian X Boran and 20 Si mmental X Boran) were stratified in a 2 X 2 diet X work factorial expe riment (not working-not supplemented, NWNS; not working-supplemented, NWS; working-not supplemented, WNS; and working-supplemented, WS). Wor king cows pulled sledges 100 days/year (pull = 350 to 450 N, 4 h/day, 4 days/week). Work output of supplemented and non-supplemented cows te as similar over 1 and 2 years. Over all 3 years, dry-matter intake rel ative to metabolic body size (g/kg M(0.75)) was greater for working, c ompared with non-working cows. Body-weight changes and body condition score were similar for working and non-working cows. Non-supplemented cows lost weight throughout the first 2-year period, while supplemente d cows tended to maintain or gain body weight over 1 and 3 years. Over 2 years, supplementation of working cows proportionately reduced live -weight loss by 0.73 and doubled the number of conceptions and parturi tions. Days in milk, milk, milk fat and protein yields were similar fo r working and non-working cows, but were greater for supplemented, com pared with non-supplemented, cows. Total conceptions and calves born i n all 3 years tended to be greater for supplemented and non-working co mpared with non-supplemented and working cows. A productivity index (P I) that took into account food intake was calculated. The PI for suppl emented cows over 2 years was greater than that for non-supplemented c ows. Meanwhile the PI was similar for working and non-working cows ove r all periods considered. A similar PI for working and non-working cow s under supplementation indicates potential of on-farm adoption of a c ow traction technology that includes improved food production and feed ing strategies.