The Poisson process as a model for compartment digesta flow in ruminants.

The Poisson process, the simplest stochastic flow process, was used to develop a multicompartment model of ruminant digesta flow with Gamma distributed retention times. Although mathematically the model is a generalization of many previously published models, the physiological model differs substantially in asserting that the distributed delay time and the exponential rate (scale) parameters, including the scale parameter of the Gamma distribution, are determined by total digesta flow, and thus invariant with respect to the fraction marked. The shape factor of the Gamma distribution is shown to be sufficient to explain the difference between markers in rate of marker excretion. Consequently, the parameters of multiple markers can be simultaneously estimated with the constraint that the exponential scale parameters and the delay time are invariant with respect to marker. This constraint leads to a measure of pure error to strengthen statistical tests for model rejection. Steady-state digesta retention time is estimated from the transient marker retention parameters, eliminating the necessity of speculating on what fraction of digesta the marked fraction represents. Tests of various models, using simulations and animal experiments indicate that, even if a model is correct, it is not possible to obtain reliable parameter estimates by fitting to a single marker. Even with multiple markers some caution must be used in interpreting parameter estimates derived from least squares fitting.

Profitability of replacing milk with a concentrate for calves of cows requiring calf at foot for milking.

During a 90-d study in Mali, West Africa, 18 zebu and zebu by Montbeliard calves, age 50 +/- 23 d (youngest pair 3 weeks), weighing 30 +/- 7 kg, under farmer management, were used to test the profitability of replacing suckled milk by a maize-groundnut cake-rice bran concentrate fed dry. During the first 45 d period there were no differences in responses of calves receiving concentrate (E) and calves suckling according to the traditional strategy (C). During the second 45 d period, milk offtake was greater for E calves, 2.34 vs. 1.77 l/d; milk suckled was less for E calves, 0.39 vs. 0.95 l/d; and average daily gain was greater for E calves, 442 vs. 139 g/d. Average concentrate consumption was 0.74 kg/d. Concentrate was compounded of locally available byproducts and cost 85 francs/kg. Considering milk sold as the only benefit, net return to unit feed cost for E calves was 1.24 and for C calves 0.81. Adding the value of the weight gain, E calves gave a 1.61 return and C calves gave a 0.98 return.

Effects of energy supplementation on lamb production of Javanese thin-tail ewes.

A 3-yr study was conducted in North Sumatra, Indonesia, as part of an evaluation of the feasibility of integrating sheep and rubber production. The objective was to evaluate the effects of increasing energy supplementation on reproduction and other performance criteria of Javanese Thin-Tail sheep grazing volunteer forages under 8- and 14-yr-old rubber trees. The control group was unsupplemented. The medium group was supplemented with high-energy feeds at 1% of the flock body weight, with the low and high groups receiving 60% or 140% of the daily energy provided by the medium group diet. Supplements provided 1.2 g protein per kilogram BW. There were 158 lambs born to the 152 ewes in the 1st year of the study. Preweaning mortality rates of lambs were reduced (P less than .01) with supplementation (45 vs 12, 3 and 12% for the control, low, medium and high groups, respectively). During the 3 yr, litter size was higher (P less than .01) in the high group (1.33, 1.31 and 1.34 vs 1.71 for ewes on the four respective diets). Observed repeatability of litter size of individual ewes in all treatment groups for the first three parities was higher (P less than .01) than would be expected if litter size were a random event. Of the lambs born in the 1st yr, kilograms of lamb weaned per ewe joined were 3.1, 7.8, 7.3 and 9.8. At prevailing prices, only the high supplement level was profitable compared to the control. For the high group, the added return from the sale of lambs born the 1st yr was 120% of the added cost of supplementing the ewes until all the lambs were weaned (15 mo). Response of sheep to the high level of energy supplementation, especially with regard to litter size, indicates that supplementing sheep grazing in rubber plantations at a high level can be profitable.