Effect of blood metabolites, body condition and pasture management on milkyield and postpartum intervals in dual-purpose cattle farms in the tropicsof the State of Veracruz, Mexico

Research was conducted on typical smallholder farms with dual-purpose cattl e (DPC) (Bos indicus x B. taurus) in the coastal north-central area of Vera cruz, Mexico. The study was divided into two phases. The aim of the first p hase was to investigate the effect of blood metabolites, body condition and pasture management on milk yield and postpartum intervals, in order to inv estigate if the former are suitable indicators of the reproductive and nutr itional status of DPC. One hundred and sixty-five calvings of crossbred cow s were recorded from January 1992 to November 1994 on 12 small farms. Milk samples were collected twice a week for progesterone analysis. Blood sample s and BCS were taken once a month. However, in Phase II emphasis was placed on the effect of pasture management upon reproductive and productive perfo rmance of DPC. Records of four farms were obtained from June 1995 to Novemb er 1996. Stocking rates were 0.40, 0.87, 0.35 and 1.5 cows/ha for farms A, B, C and D, respectively. Farms A and C used a slow rotation while B and D used a rapid rotation. In Phase I, the changes in BCS during the last month of pregnancy and first month postpartum did not correlate (p>0.05) with mi lk yield or reproductive performance. Blood the metabolite profiles were no t consistently related to productive or reproductive variables. The effect of farm and season was significant (p<0.05) on most of the response variabl es and low productivity on overstocked farms lead to the conclusion that th e low reproductive performance of DPC was linked to poor pasture management . During Phase II, farms A (FA) and D (FD) produce more milk than the other s. Days to first service, days open, and carving interval were similar for farms B (FB) and C (FC), highest for Farm A, and lowest for Farm D. The for age availability mean was above the critical range of 6-8 kg of city matter per 100 kg of liveweight (kg DM/100 kg LW) in all Farms (range from 6.1 +/ - 5.0 to 21.1 +/- 11.2 kg DM/100 kg LW). Farm D had the highest stocking ra te (1.5 cows/ha), a rapid rotation (10 paddocks), a good forage availabilit y (7.1 +/- 3.9 kg DM/100 kg LW) with a Good quality for a tropical pasture (11.6 +/- 2.4% crude protein), and an economic energy supplementation. Thes e results suggest this type of management could be more widely employed to improve the productivity of DPC on smallholder farms in the Mexican tropics . (C) 1999 published by Elsevier Science B.V. All rights reserved.