Replacement of alfalfa hay (Medicago sativa) with maralfalfa hay (Pennisetum sp.) in diets of lactating dairy goats

The objective of this experiment was to study the effects of substituting alfalfa (Medicago sativa) with maralfalfa (Pennisetum sp.) on energy, nitrogen and carbon balance, methane emission, and milk performance in dairy goats. Ten Murciano-Granadina dairy goats in late lactation (45.7 ± 2.96 kg of body weight [BW]) were selected in a 2-treatment and crossover design experiment where each goat received both treatments in 2 periods. One group of five goats was fed a mixed ration with alfalfa as forage (A diet) and the other diet replaced alfalfa with maralfalfa (M diet) in a forage concentrate ratio of 40/60. Diets were isoenergetic and isoproteic. The goats were allocated to individual metabolism cages. After 17 d of adaptation, feed intake, total faecal and urine output and milk yield were recorded daily over a 5 d period. Then, gas exchange measurements were recorded individually by a mobile open-circuit indirect calorimetry system using a head box. Daily dry matter intake was higher on A than on M diets (1.8 vs. 1.6, for A and M respectively), but no differences was observed in metabolizable energy intake (1089 kJ/kg of BW0.75, on average). Greater values in M than A were found in rumen propionic acid (17.5 vs. 15.6 mol/100 mol, respectively) and milk C15:0 (0.81 vs. 0.62 g/100 g), C17:0 (0.33 vs. 0.24 g/100 g) fatty acids, indicating predominance of amylolytic fermentation. Milk uric acid, a potential biomarker of rumen nitrogen flow and feed efficiency, was higher in A than M (133 vs. 102 μmol/L). Higher milk yield (1.8 vs. 1.7 kg/d) and CH4 emissions (28.5 vs. 25.9 g/d) in A compared to M diet were observed, respectively. Use of tropical grasses such as maralfalfa in temperate climates could be a strategy for farmers to incorporate forage into feed for flocks, as milk chemical composition did not change markedly and maralfalfa inclusion reduced CH4 emissions by goats (although this reduction did not occur in CH4 emission compared to dry matter intake and milk yield).