Effect of complex catalytic supplementation with non-protein nitrogen on the ruminal ecosystem of growing goats pasturing on shrub land in Mexico

Abstract

Thirty-eight young Alpine goats, 16.1 (±0.370) kg body weight (BW), were reared at Querétaro, Mexico, grazing on a semi-arid woody brush ( Caducifolio espinoso) range land. The experimental goats ( n = 20) were pastured daily and supplemented with 200 g/day of a complex catalytic feed (CCF). It consisted of molasses (14–18%), urea (8–10%), salt (3–4%), limestone (3–4%), cottonseed meal (13–18%), rice polishing (10–13%), corn (11–12%), poultry litter (9–10%), commercial mineral salt (1.3%), ammonium sulfate (0.3–0.5%), cement kiln dust (1.5%), and animal lard (10–15%). The control goats ( n = 18) were supplemented daily with 300 g of a balanced concentrate (BC), containing 1.5% commercial mineral salt, 60% corn, 32.5% wheat bran, and 4% soybean oil meal. Stocking rates varied from 1.45 to 1.85 AU/ha and daily stocking rate from 36.4 to 58.6 AU/ha. At all times, fibrous forages were available exceeding the voluntary dry matter intake. One fistulated goat was kept in each group. Growth of the experimental goats averaged 95 g/day (±3) compared to 76 g/day (±5) of the controls ( P < 0.005) in 150 days from June to November. Supplementation per kg BW was from 17.5 to 10.4 g BC/day for the control goats; the experimental goats received 12.2–6.5 g CCF/day. Weight gain in response to fermentable carbohydrates (FC) averaged 8.95 g BW gain/g FC/day for the control BC goats, compared to 28.2 g BW gain/g FC/day for the experimental CCF goats. Daily supplies of FC to goats on CCF supplementation were always below the limits for celullolysis at 6 g/day, while FC supplies of BC rations to the control goats always exceeded them. After 2 h of shrub land pasture, the ruminal pH rose when CCF was offered and stayed above 6.6 during 12 h, while the ruminal acidity in BC goats went down to pH 5.57 at 6 h and rose to 6.5 by 12 h. Ammonia (NH 3 mg/l) in ruminal liquid of CCF goats was higher ( P < 0.01) in average and all but one sample. Total cost per animal per day including shrub land pasture, management, medicine and salaries was US $0.06 for experimental goats and US $0.09 for controls (market price for goat meat was US $1.15/kg; US $1.00 = 10 Mexican Pesos, November 1998). Daily gain varied during the study period from 77 to 85 g/day in BC control goats compared to 92–97 g/day in experimental CCF goats. CCF supplementation to shrub land pasturing resulted in significantly greater weight gains apparently due to elevated ruminal pH, higher availability of fermentable carbohydrates and ruminal ammonia, augmenting ruminal ecosystem, digestibility and voluntary feed intake. The use of local shrub land resources and complex catalytic supplementation with non-protein nitrogen provided greater profitability from this feeding system for growing goats than the traditional balanced concentrate feed supplementation.