ME and MP requirements of goats for gestation from day 95 to parturition are based on pregnancy tissue growth curves and composition determined with sheep, litter size (1, 2, or 3), and birth weight per kid. An efficiency of ME use for gestation of 0.133 (AFRC, 1998) was assumed, as well as an efficiency of MP use of 0.33 (NRC, 2001).
MP requirements are preferable compared with CP because they consider how feedstuffs vary in the extent to which proteins are degraded in the rumen (or the extent of passage to the small intestine of intact feed protein) and dietary and animal characteristics that impact the quantity of microbial protein that is synthesized in the rumen and flows to the small intestine.
However, in many instances there may not be adequate knowledge about these dietary properties to directly predict the amount of MP resulting from a given level of consumption of a particular diet. If such information is know, then the Calculator entitled "Metabolizable Protein (MP) Intake Based on Estimates of Ruminally Undegraded Protein (UIP) and Microbial Protein Synthesis" can be employed. If not, then a simple means of determining how requirements for MP relate to those for CP can be used. In this regard, NRC (2000) suggested that MP requirements can be reasonably well translated or projected to CP needs for most practical purposes with some assumptions regarding the extent of ruminal degradation of dietary CP. It was suggested that CP requirements can be determined through dividing MP needs by values from 0.64 to 0.80, which apply to diets with 0 and 100% UIP, respectively. Typically, diets with 0 or 100% of CP degraded (or undegraded) in the rumen are not fed. Thus, CP requirements have been calculated from MP for diets containing CP that is digested in the rumen (DIP; degraded intake protein) with extents of 80, 60, and 40%, which equates to concentrations of UIP of 20, 40, and 60%, respectively. A diet with 20% UIP would probably be one of fresh forage that typically has CP extensively degraded in the rumen. A diet with 40% UIP might be one with a mixture of concentrate (e.g., high level of corn) and forage. A diet with 60% UIP would have a moderate to high level of concentrate, and perhaps with some feedstuffs such as blood, feather, fish, or corn gluten meals that have considerable protein that passes from the rumen intact. Likewise, pelletizing usually increases the dietary UIP concentration.
In our example, the requirement for ME on day 135 with a birth weight of 3 kg and litter size of 1, 2, and 3 is 3.22, 5.02, and 6.81 MJ, and that for MP is 37.1, 60.0, and 82.8 g, respectively. Also for our example, the gestation CP requirement for a litter size of 2 is 89.2, 85.2, and 81.5 g/day for diets with a UIP concentration of 20, 40, and 60%, respectively.