VOLUNTARY DRY-MATTER INTAKE BY DAIRY GOATS GRAZING ON RANGELAND OR ONAGRICULTURAL BY-PRODUCTS IN MEXICO

Voluntary dry matter intake (VDMI) by dairy goats was estimated using the fill unit system determined by sex, live weight, level of producti on, stage of lactation and pregnancy. Forage fill units for each feed offered were obtained from crude fiber (CF) and digestibility of organ ic matter (OMD). Equations accounted for the interaction between forag es and concentrates. From 1988-1992, 668 lactations were studied to de termine the VDMI by dairy goats under a management system using confin ement or pasture grazing. A goat of 55 kg BW in mid-lactation (2 kg mi lk/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 essa yed 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 req uired 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 d airy goats. In the five year study, 45 control dairy goats in full con finement produced, per year, an average of 474 kg (SD+/-35) milk durin g 260 d of lactation (SD+/-5), milked manually once a day. Goats consu med yearly 764 kg (SD+/-15) of dry matter (DM), 413 kg (54%) forage an d 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 lacta tions were examined in dairy goats fed agricultural by-products or gra zing 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%) concen trates and 659 kg (78%) of various forages. This second mixture averag ed 2.1 Mcal ME/kg DM. The yearly total energy needs were 1630 and 1585 Meal 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, i n the pastured animals only, a second peak in milk production accompan ied by an increase in VDMI. This study proved that it was possible to produce goat's milk economically, fed agricultural by-products and ran geland vegetation, that otherwise would be wasted. Rangeland was graze d seasonally, when vegetation growth permitted, and left idle in the d ormant period.