Voluntary dry matter intake by dairy goats grazing on rangeland or on agricultural by-products in Mexico

Abstract Voluntary dry matter intake (VDMI) by dairy goats was estimated using the fill unit system determined by sex, live weight, level of production, stage of lactation and pregnancy. Forage fill units for each feed offered were obtained from crude fiber (CF) and digestibility of organic matter (OMD). Equations accounted for the interaction between forages and concentrates. From 1988–1992, 668 lactations were studied to determine the VDMI by dairy goats under a management system using confinement or pasture grazing. A goat of 55 kg BW in mid-lactation (2 kg milk/d) was considered as standard. A forage of 15% crude protein (CP), 25% CF and 77% OMD was the basis of comparison. Three levels were essayed to estimate VDMI: low 100 g/ kg, medium 120 g/kg and high 140 g/kg metabolic W 0.75 . Each VDMI predicted was correlated to the energy required for different production stages. Results showed a VDMI of 140 g/kg W 0.75 to have the highest correlation to energy needs of Mexican dairy goats. In the five year study, 45 control dairy goats in full confinement produced, per year, an average of 474 kg (SD ± 35) milk during 260 d of lactation (SD ± 5), milked manually once a day. Goats consumed yearly 764 kg (SD ± 15) of dry matter (DM), 413 kg (54%) forage and 351 kg (45%) concentrates. This mixed diet provided an average of 2.5 Mcal ME/ kg DM. On the other hand, during the time studied, 623 lactations were examined in dairy goats fed agricultural by-products or grazing rangeland with supplementation. They produced yearly 385 kg (SD ± 154) milk, with an average of 256 d (SD ± 32) of lactation and a VDMI of 845 kg DM (SD ± 23). This feed was composed of 186 kg (22%) concentrates and 659 kg (78%) of various forages. This second mixture averaged 2.1 Mcal ME/kg DM. The yearly total energy needs were 1630 and 1585 Mcal in confinement and pasture, respectively, with 57% and 32% being supplied by the concentrates in each case. Concentrates (22% offered) played a key role all year for milk production in grazing, supplying 32% of total energy and 44% of protein requirements. Results showed, in the pastured animals only, a second peak in milk production accompanied by an increase in VDMI. This study proved that it was possible to produce goat's milk economically, fed agricultural by-products and rangeland vegetation, that otherwise would be wasted. Rangeland was grazed seasonally, when vegetation growth permitted, and left idle in the dormant period.