Energy intake is the most limiting factor for milk production. Like the dairy cow, the lactating goat is able to draw upon body reserves in early lactation to meet energy requirements when feed intake lags behind nutrient demand. In early lactation, energy derived from body reserves is utilized more efficiently than feed energy for milk production. These body stores can be replaced during mid- and late lactation and in the dry period. The rate and extent to which a dairy goat is capable of drawing upon body reserves to meet the energy requirement in early lactation is critical in determining her ability to produce and sustain a high level of milk production. In addition, the ability to replenish body stores has a direct impact on the ability to conceive later.
It has not been clearly established when replenishment of body stores is most efficient or what is the optimal time pattern of tissue replenishment during late lactation and the dry period. This most likely varies with conditions such as the quantity of tissue lost earlier. From a strictly energetic point of view at particular points in time, the efficiency of energy use in tissue replacement is greater in late lactation than in the dry period, suggesting that most body weight and condition restoration should be in late lactation. However, if energy required for tissue maintenance is independent of or at least not closely associated with body composition, then the efficiency of energy use might be greater for replenishment during the dry period. Dry period tissue gain rather than in late lactation would result in a minimal period of time during which tissue must be maintained before freshening. Furthermore, in the period immediately preceding parturition and lactation, to achieve highest lactation performance, it is imperative to prepare the doe for lactation demands, such as increased energy intake to increase ruminal papillae development, which lends itself well to dry period tissue replenishment.
The ability of the doe to replace energy stores in late lactation or in the dry period is obviously affected by dietary energy density. Body tissue replacement increases with increasing dietary concentration of digestible energy or concentrate level, but at excessively high energy densities fattening may result from a shift in nutrient partitioning, reducing reproductive performance and increasing periparturient health problems, such as fatty liver. The present nutrient requirements provided by the National Research Council do not adequately address dietary energy density in late lactation or in the dry period. Information is needed on the optimal digestible energy density in late lactation and in the dry period so that body stores are replenished most efficiently to avoid over-conditioning and to maximally prepare does for the onset of lactation. Overall, current information available indicates that most body energy stores used in early lactation should be replaced in the late-lactation period. European recommendations are that starting in the fourth month of lactation, multiparous and primiparous goats -- does and doelings, respectively -- should gain live weight at approximately 2.6 and 4.9 pounds per month, respectively. Future research at the E (Kika) de la Garza Institute for Goat Research will investigate whether there are economic advantages of differences in the time when tissue lost in early lactation is replaced.
Reference: Sahlu T. and A. Goetsch. 1998. Feeding the Pregnant and Milking Doe. Pages 4-20 in Proc. 13th Ann. Goat Field Day, Langston University, Langston, OK.