Effect of feeding almond hulls on energy partitioning, nutrient balance, milk yield, and methane emissions in lactating dairy goats

Almond hulls are a rich source of triterpenoids (betulinic, urosolic, and oleanolic acids), flavonols, phenolics, catechins, and other polyphenolic compounds, some of which have antibacterial and antioxidant activity. The aim of this study was to evaluate the effects of incorporating almond hulls into the compound feed of diets for dairy goats on milk performance, methane emissions, and energy partitioning. Ten Murciano-Granadina dairy goats (n = 5/group) in late lactation were used in a crossover design experiment (2 treatments across 2 periods). In the concentrate of the test diet (ALH), almond hulls were included at 12% of DM replacing (DM basis) 6.4% barley grain and 8% (DM basis) wheat bran in the control diet (CON). Diets were isoenergetic, and addition of 0.35% urea to the ALH diet rendered it isonitrogenous relative to CON. After 14 d of diet adaptation, goats were allocated to individual metabolism cages for another 7 d. Feed intake, total fecal and urine output, and milk yield were recorded daily for the next 5 d and ruminal fluid was collected in the last day before goats were moved to calorimetry chambers. Gas exchange was measured for each goat during 24 h using a mobile open-circuit indirect calorimetry system with 2 head boxes (a total of 5 d period). No differences in DM intake (887.5 g/d, on average) and ME intake (633 kJ/kg of BW^0.75, on average) were detected, and both groups were in negative energy balance. Correcting the energy balance to zero reserve mobilization, the efficiency with which ME intake was converted into milk was 0.63. Although no differences were observed in milk production (1.48 kg of milk per goat per day, on average), when expressed in terms of FCM, a greater feed efficiency was observed in the ALH group (2.12 vs. 1.97, respectively) due to greater milk fat concentration in the ALH group (8.9% vs. 7.3%). There was no difference due to diet in terms of methane (CH₄) production, with an average of 18.8 g/d. However, when CH₄ was expressed relative to milk fat yield, goats in the ALH had lower values (191 vs. 244 g CH₄/kg milk fat for ALH and CON). Overall, the inclusion of almond hulls at 7% of DM in the diet had no negative effects on milk production or diet digestibility, but because composition and quality of almond hull varieties can vary greatly (e.g., moisture and ash content), attention is needed when evaluating the inclusion of this byproduct feed in the diet of lactating goats.