Recently weaned calves have mature rumen function within 2-3 weeks after dry feeds are introduced (Lalles and Poncet 1990 {615}; Lalles and Poncet 1990 {605}). When crushed peas replaced soybean meal in the diet of 7-20 week old calves that had recently been weaned, both diets had similar effects on intake, liveweight and gain (P > 0.05; table 4). It was concluded that the protein degradability of peas and soybean meal in the rumen had little effect on the performance of recently weaned calves (Lalles and Poncet 1990 {605}). In fact, ruminal N degradation (73%) and OM digestibility (64%) of the pea diet was unaffected by age, but increased (47-74%for N degradation and 50.7-71.2% OM digestibility) for the SBM diet. This indicates a more rapid ruminal adaptation to the pea diet (Lalles and Poncet 1990 {605}). A mature N metabolism for both diets was evidenced by similar volatile fatty acid concentrations in the rumen and blood, 65% of microbial N in the duodenal N flow and efficient microbial N synthesis (24 g microbial of N synthesized per kg truly fermented OM) (Lalles and Poncet 1990 {605}). The amino acid compositions of feed, duodenal and ileal digesta were similar between SBM and pea meal fed calves. However, ileal methionine levels were higher (P < 0.01) in the pea meal diet than in the SBM diet. Plasma free amino acids, asparagine, valine and leucine were higher (P < 0.05) and glutamine was lower (P < 0.01) in SBM fed calves compared to pea fed calves (Lalles et al. 1990 {606}). Other studies report no difference in nutrient digestibility, nitrogen retention or blood values when replacing peas for SBM in young weaned cattle (Szyszkowska et al. 1987 {653}).
Feeding a diet containing yellow peas or SBM to young cattle (21-120 d) did not significantly effect nutrient digestibility, nitrogen retention or carcass dressing percentage. It was concluded that the level of peas should not exceed 35% or 0.8 kg/d (Namiotkiewicz et al. 1989 {623}). In contrast, Namiotkiewicz et al. (1989 {629}) reported a slight reduction in fat and crude protein digestibility and N retention when extruded ground yellow peas replaced SBM in the prestarter/starter concentrates that were fed to 24-120 d old calves. Fiber digestibility was increased with the supplementation of ground yellow peas. This slight reduction in CP digestibility and N retention did not affect animal performance (Namiotkiewicz et al. 1989 {629}).
Unlike the preruminant calf that depends greatly on the type of protein and the quantity and quality of amino acids for growth, the weaned ruminant calf relies more on the introduction of dry feed and the development of a functional rumen (Lalles et al. 1990 {606}). Peas can act as the sole protein source for young ruminants that have a functioning rumen with little or no effect on performance.
| Table 4. Performance of young recently weaned calves (7-10 weeks) fed crushed pea or soybean meal (DM) + 20% hay diets that were isoenergetic (11.7 MJ metabolizable energy kg-1 DM) and isonitrogenous (18% CP) | ||
|---|---|---|
| Crushed pea | Soybean meal | |
| Feed Intake (g DM day-1) | ||
| 9-10 week | 804 | 814 |
| 15-16 week | 1410 | 1457 |
| 19-20 week | 2352 | 2253 |
| Liveweight (kg) | ||
| 9-10 week | 68.2 | 69.6 |
| 15-16 week | 76.7 | 77.3 |
| 19-20 week | 96.5 | 98.2 |
Adapted from Lalles and Poncet 1990
{605}.