Variability in Voluntary Intake of a Molasses-based Supplement by Cows and Calves

Supplements are often fed to ruminants in extensive grazing situations to provide minerals and nitrogen likely to be deficient in pasture. However a large proportion of animals offered such supplements may not consume any supplement, while among consumer animals the variability in supplement intake may be high (Wheeler et al., 1980; Dixon et al., 1998). An experiment examined the distribution of intake of a molasses-based supplement containing phosphorus and urea in a breeder herd. A herd of mixed-age breeder cows, calves, heifers and bulls were offered ad libitum a molasses-based supplement containing 13% urea and 17% phosphoric acid. After 2 weeks lithium-labelled supplement (2 mg Li/kg LW) was offered on one day to measure individual intakes of supplement. The molasses was offered in three 560 mm diameter feeders placed together near the water point.

Variability in Voluntary Intake of Loose Mineral Mix Supplements by Grazing Heifers

Loose mineral mix (LMM) supplements are often fed to ruminants in extensive grazing situations to provide minerals and nitrogen likely to be deficient in pasture. However a large proportion of animals offered such supplements may not consume any supplement, while among consumer animals the variability in supplement intake may be high (Wheeler et al., 1980; Dixon et al., 1996). Two experiments examined the distribution of intake of LMM supplements offered to heifers grazing in mob and paddock sizes representative of commercial cattle properties.

Using Alkanes to Predict Voluntary Intake, Faecal Output and Digestibility of Buffel Grass Hay Fed to Steers

The cuticular waxes of forage plants contain long chain n-alkanes with odd carbon chain lengths in the range C25-C37 which are quantitatively recovered in faeces. When these concentrations are used with the concentrations of administered synthetic even chain length alkanes, the voluntary intake (VI), faecal output (FO) and digestibility (DMD) of forages can be estimated (Dove and Mayes 1991, 1996).

Controlling voluntary intake of molasses-based supplements in grazing cattle

Molasses-based liquid supplements fed ad libitum are widely used to provide additional metabolisable energy, non-protein N (NPN) and other nutrients to grazing cattle, but it is often difficult to achieve target intakes of supplementary nutrients. Experiments examined the effects of increasing concentrations of phosphoric acid, urea and ammonium sulfate on the voluntary intake (VI) of molasses-based supplements offered ad libitum to heifers grazing tropical pastures. In Experiment 1, the VI of a supplement containing 78 g urea/kg and 26 g phosphoric acid/kg as-fed (M80U+PA) was 3.61 g DM/kg liveweight (LW) per day, and provided 181 mg NPN and 32.4 mg phosphorus (P)/kg LW per day. Increasing the urea content of the supplement to 137 g/kg (M140U+PA) or 195 g/kg (M200U+PA) reduced VI of supplement DM, NPN and P by up to 76%, 44% and 80%, respectively. VI of supplement containing ammonium sulfate (M140+AS+PA) was lower (P < 0.05) than that of M140U+PA supplement, and tended (P > 0.05) to be lower than that of M200U+PA supplement. In experiment 2, the VI by heifers of a supplement containing 200 g urea/kg (M200U) was 1.53 g supplement DM/kg LW per day, which provided 186 mg NPN/kg LW per day. Inclusion of 49 g phosphoric acid/kg as-fed in this supplement (M190U+50PA) reduced (P < 0.05) VI of supplement DM and NPN by 33% and 36%, respectively, while inclusion of 97 g phosphoric acid/kg (M180U+100PA) reduced (P < 0.05) VI of supplement DM and NPN by 43% and 48%, respectively. The M190U+50PA and M180U+100PA supplements provided 16 and 26 mg P/kg LW per day, respectively. Heifers not fed supplements gained 0.07 kg/day, and the M200U supplement increased (P < 0.05) LW gain to 0.18 kg/day. LW gain was further increased (P < 0.05) by the M190U+50PA to 0.28 kg/day, indicating a growth response to supplementary P. No adverse effects of the supplements on animal health were observed in any of the experiments. In conclusion, addition of urea and/or phosphoric acid to molasses supplements effectively reduced VI of supplementary DM, NPN and P, and in the circumstances of Experiment 2, both molasses-urea and P supplements increased heifer LW.

Inclusion of cottonseed meal into loose mineral mix supplements increases the voluntary intake of the supplement by grazing heifers

Loose mineral mix (LMM) supplements based on ingredients such as salt, urea and minerals offered ad libitum are widely used to provide additional nutrients to grazing cattle, but it is often difficult to achieve target intakes. An experiment with heifers grazing mature tropical pasture examined the effects of substituting 80, 160 or 320 g/kg of the salt in a LMM supplement with cottonseed meal on the voluntary intake of the LMM supplements by paddock groups of heifers over 10 weeks. Average voluntary intake of a LMM containing (g/kg) 640 salt, 300 urea and 60 ammonium sulfate (40.2 g DM and 6.14 g total nitrogen/day) was increased linearly (P < 0.001) to 50.8 g DM and 8.88 g total nitrogen/day when up to 320 g/kg cottonseed meal was substituted for salt in the LMM. This increase in intake of nitrogen in LMM was due to the increase in voluntary intake of the supplement rather than the increased nitrogen concentration of supplement. The distribution of daily intake of supplement within paddock groups of heifers was estimated during Weeks 5 and 10 using supplements labelled with lithium sulfate. Neither the coefficient of variation within paddock groups of heifers in supplement intake (mean 96%), nor the proportion of non-consumers of supplement (mean 17%), was changed (P > 0.05) by substitution of salt with cottonseed meal. In conclusion, the inclusion of a palatable protein meal into LMM increased the voluntary intake of this type of supplement.

Alkane Profiles in Tropical Forages

The role of n-alkanes in animal nutrition research has recently been reviewed by Dove and Mayes (1996). The measurement of voluntary intake (VI) using the naturally occurring odd chain length alkanes C31 or C33 in conjunction with administered even chain length alkanes such as C32 and C36 provides several advantages over the more conventional methods. Much of the development work involving this technology has been carried out with sheep or dairy cattle fed predominantly temperate pasture. Laredo et al., (1991) have published alkane profiles for a number of introduced tropical pasture grasses but no alkane profiles have been published for native tropical pasture grasses. Animal production for a consuming world : proceedings of 9th Congress of the Asian-Australasian Association of Animal Production Societies [AAAP] and 23rd Biennial Conference of the Australian Society of Animal Production [ASAP] and 17th Annual Symposium of the University of Sydney, Dairy Research Foundation, [DRF]. 2-7 July 2000, Sydney, Australia.