Cow Performance in Conventional Versus Early Weaning Herds in North Patagonia, Argentina

Abstract

This paper demonstrates that early weaning should be included as an important management guide line in raising cattle in north Patagonia, Argentina. At most ranches, breeding takes place all year long. This makes it difficult to establish the weaning per centage (number of calves obtained per hundred bred cows). However, the calf-cow relationship, obtained from agrarian censuses and vaccination campaigns against aphthous, shows weaning values close to 60%, with variations between 55% and 72%, depending on zone and year. Another consequence of continuous breeding and lack of enough paddocks is the premature pregnancy of young cows, which is harmful for their growth and subsequent pregnan cies. Lack of adequate equipment, fences, watering points, etc. constrains proper use of renewable natural resources, with overgrazing in some cases and undergrazing in others. This is accompanied by a reduced livestock production. However, there exists low-cost technology adequate for these production systems, which allows one to improve cattle raising productive indices and rangeland vegetation productivity.1 An average weaning of 90% (84% to 100%) and a weaning weight of 195 pounds (180 pounds to 200 pounds) was obtained in an eight-paddock rotational grazing system, which had a 3-mo (November, December, January) breeding season during late spring-early summer from 1988 to 1993.2 Early weaning is defined as calf weaning at 2 mo, with the calf weighing between 154 and 177 pounds. Conventional weaning is defined as calf weaning at 6 mo. The advantages of an early weaning include 1) improvements in cow body state and pregnancy, especially in young cows of second parturition; 2) attenuation of emergency situations (i.e., scarcity of forage, reproductive problems because of a bad body condition, etc.); and 3) stocking rate increases. It is impo tant to clarify the term body, indicating either state or condition: animals are classified using a scale according to their fatness. In this work, a scale from 1 to 9 was used, where 1 corresponds to an extremely thin cow and 9 to a fat cow.3 Cow observations at the time of parturition, breeding, or tact (determining whether or not the cow was pregnant) allow proper management changes in time (i.e., a paddock change of the whole herd, a separation of cows in worst state from the herd, etc.). Cow body condition at parturition is related to the amount of days until breeding time and milk production. Cow state at breeding time influences the number of times that cow is ready for breeding until it becomes pregnant, and the time between parturitions. During breeding, consumption must not be restricted because cows are suckling calves and they have to maintain a good body condition to become pregnant. The period of suckling has an adverse effect on reproduction. Lusby and Wettemann4 determined that weaning 2-yr-old cows of first parturition with very poor body condition (3 to 43), increased pregnancy from 57% to 97% between 6 to 8 wk after partu rition. A pregnancy increase of 16% in 3-yr-old cows, and 28% in mature cows, was reported by Guyer5 when weaning was done 8 d before breeding. Early weaning in mature cows with a body condition of 5, when compared with co ventional weaning,1 shortened the period parturition new pregnancy from 81 to 46 d, and increased pregnancy per e tages from 83% to 100%.6