عنوان مقاله [English]
Introduction Global demand for goat milk and its products has been growing. The decreased pasture quality has led goat producers to use intensive production systems with economical fodder resources. Goat milk contains functional compounds that enhance human immune system and overall health. Goat milk is enriched with functional peptides, conjugated linoleic acid, and healthy oligosaccharides that can immensely benefit human immunity and health. Goats are usually capable in utilizing lower quality forages. In few recent studies, alfalfa hay was compared with different by-products and local feeds with no significant effects found on rumen fermentation and milk production or composition. Murciano-Granadina goats were capable to utilize low quality fiber sources towards milk production.
The objective of this study was to determine effects of feeding various forage sources on milk production, nutritional behaviors, and blood parameters of Murciano-Granadina dairy goats in Iran.
Materials and Methods Thirty second-parity Murciano-Granadina goats (190 ± 3 days in milk; 2 ± 0.03 kg/d milk yield) were used in a completely randomized design study with three treatments (10 goats per treatment). Treatments were diets containing 1) wheat straw (WS), 2) alfalfa hay (AH), or 3) corn silage (CS). To enable sound comparisons among forage sources, treatment diets were balanced to be isoenergetic and isonitrogenous. The concentrate portion of the rations was similarly ground for all treatments. Feed and milk (from a.m. and p.m. milking) samples were collected weekly for later analytical measurements. To determine goat behavior time; eating, ruminating, and resting times were observed and recorded by technical individuals on days 30 and 50 of the experiment in two 24-h period. Blood samples were taken at 0800 h on d 1, 30, and 56. The data were analyzed using mixed models of SAS program.
Results and Discussion The dry matter intake (DMI) was significantly affected by treatments (P <0.001). Body weight and its changes were similar among treatments, suggesting that nutrient partitioning towards tissue accretion or depletion was not different among treatments during the study, since goats were in late lactation. However, DMI was 228 g higher for goats received diet containing corn silage than for those received AH (P < 0.05). Decreased DMI for diets with wheat straw and alfalfa hay compared with corn silage could at least partially be related to increased dietary fat and indigestible cell wall in the former diets. Ruminating, standing, and resting times were not different among treatments (P > 0.10). These data would suggest that despite the differences in forage nutritional characteristics, digestibility, and intake, ruminating time was similar among treatments.
Goats fed CS had higher milk production than the other two groups (P <0.001). The percentage of milk fat in the alfalfa hay treatment was higher than in the other treatments (p> 0.05). Similar to milk volume, daily yields of milk protein, lactose, and total solids were also higher for corn silage than for other treatments. This could be a result of increased milk volume and unchanged milk contents of protein and lactose for corn silage. Milk fat content was higher (P < 0.01) for AH treatment but milk fat yield tended (P < 0.10) to be greater for CS treatments than for other treatments.
Serum concentration of glucose, albumin and non-esterified fatty acids (NEFA) were not significant among experimental treatments. Glucose and NEFA values are usually interpreted as indices for energy status of experimental animals. Similar glucose and NEFE concentrations in blood for the three forage treatments could be evaluated in light of the fact that goats were in mid and late lactation and thus were not in negative energy balance. As a result, they may have not been metabolically sensitive enough to respond to treatments at this stage of lactation. Serum concentrations of total proteins were higher for AH than for other treatments (P < 0.05).
Findings of this study suggest that lactating Murciano-Granadina goats are capable to utilize different forage sources including alfalfa hay, corn silage and wheat straw. However, corn silage leads to higher raw and fat-corrected milk yields, whereas alfalfa hay increases milk fat content. For higher feed efficiency and lower feed cost and where more available, Wheat Straw may be used in Murciano-Granadina goat diets. To improve milk yield and fat content and yield simultaneously, certain combinations of alfalfa hay and corn silage may be required. Determining this will require future experimentation. Future experiments could also investigate forage choice effects on milk fatty acids profile and other functional compounds.