Replacement bucks and does must gain sufficient weight from weaning to breeding to be adequately large and sexually mature. A Spanish doe weaned at 12 weeks of age would be expected to weigh 40 pounds and gain 5 pounds per month to achieve a minimum breeding size of 60 pounds at 7 months of age. A Boer doe weaned at 12 weeks of age would be expected to weigh 50 pounds and would need to gain 7.5 pounds per month to be 80 pounds at breeding. These are minimum weights, and it is advantageous for animals to be slightly heavier. Some purebred breeders wait to breed their doelings at 19 months of age because a doe with a bigger frame size is desired. Most commercial goat producers cannot afford the cost of an extra year of maintaining an animal with no production.
Does will generally gain sufficient weight if an adequate amount of a moderate quality forage is available. If doelings are not gaining adequate weight -- as measured by a scale or through the heart girth conversion program -- they could be supplemented with whole shelled corn at 0.5 percent to 1 percent of body weight per day (one-fourth to one-half pound of corn per head per day for a 50- pound doeling). Feeding excessive grain to does causes an overly fat condition. Fat may be deposited in the udder, leading to reduced formation of milk secretory tissue. The doe is also more likely to have pregnancy toxemia and birthing problems. If sufficient good quality pasture is not available, growing doelings will need good quality hay and a supplement such as whole shelled corn, sweet feed, or range cubes or pellets at 0.5 percent to 1.0 percent of body weight.
Bucklings must gain more weight than doelings to reach puberty. While there are no available recommendations for weight of meat goat bucklings at first breeding, these animals need to reach an adequate size to achieve puberty. Like doelings, their body condition should be monitored and supplemented at 0.5 percent to 1 percent of body weight per day (one-fourth to one-half pound of corn per head per day for 50-pound buckling). Most bucks do not let a lack of body weight interfere with breeding, but some body reserves are necessary to maintain fertility and mating activity throughout the breeding season.
Reference: Hart, S. 2008. Meat Goat Nutrition. Pages 58-83 in Proc. 23rd Ann. Goat Field Day, Langston University, Langston, OK.