Effect of concentrate supplementation on plasma minerals and performance of smallholder dairy cattle

An assessment of calf birth weight (CBWT), milk yield (MY) and plasma calcium (Ca), phosphorus (P) and copper (Cu) was done in supplemented (S) and control (C) cattle groups grazing tropical pastures . The supplemented group had compared to the control group higher P (5.1 vs 4.7±0.1 mg/dl; P<0.05), Cu (0.5 vs 0.4±0.02 μg/ml; P<0.001), MY (10.13 vs 7.63± 0.07 l/day; P<0.001) and CBWT (26.01 vs 23.4±0.68 kg; P<0.05). The control group showed P and Cu defi ciency and the production effect of supplementation with an appropriate mixture were was more than 0.5 kg milk per kg mixture and 10% heavier calves at birth.


INTRODUCTION
Energy is often the fi rst limiting nutrient for milk yield (MY) in the smallholder sector in the tropics because of low energy content in tropical forages (Larry and Joe, 1994) and tissue mineral concentrations and functional forms must be maintained within limits for optimum productive performance (McDonald et al., 1997).Defi ciencies of Ca and P in plasma of dairy cattle have been reported in Tanzania (Phiri et al., 1997).Gimbi et al. (2002) found out that steaming up of animals was not normally done and mineral supplementation was not regular in Rungwe.The objective of the present study was to demonstrate with farmers the response of plasma mineral concentration and productive performance of dairy cattle to concentrate supplementation.

Research design and treatments
A longitudinal study with multistage, purposive sampling was set where 3 divisions and in each 3 wards were selected.Two villages and 4 farmers per village were selected from each selected ward.A sample of 72 animals, mainly Friesian × Zebu crossbreds about 7 months pregnant was selected from the farmers and randomly allocated into control and supplemented treatments.

Feeding and management of experimental animals
Animals were managed under farmers' conditions, e.g., mainly only grazing tropical pastures, except for the S where concentrate was given in addition.Nutrients available and defi cits from basal diet were estimated (Mussa, 1998) and supplement made to cover the defi cits and enable the animals approximately meet daily allowances for ME, CP and minerals (McDonald et al., 1997) for 500 kg pregnant and lactating animals producing milk of 38 g fat and 34 g protein/kg.The supplement was made from hominy meal, sunfl ower seed cake and minerals (Super Maclick ® , Coopers Kenya Ltd.) to contain 13.4 MJ ME, 138.1 g CP, 2.3 g Ca, 1.3 g P and 19 mg Cu per kg feed DM and was fed daily at a rate of 7 g/kg Bwt for 2 months pre and post calving.

Samples, parameters, laboratory and statistical analyses
Blood samples were collected monthly starting about 60 days prepartum to 90 days postpartum.Plasma Ca, P and Cu levels were determined by spectrophotometric techniques (Kessler and Wolfman, 1964;Paynter, 1987).A weigh band was used to estimate CBWTs.Daily MY was measured and recorded by farmers.General linear model (SAS System, Release 6.08) consisting of Ca, P, Cu, MY and CBWT as dependent variables and treatment as an independent effect was used for statistical analysis.

Plasma mineral concentration, milk yield and calf birth weight
There was a small insignifi cant difference in mean Ca values between the S and C (Figure 1; Table 1).The mean P concentration for the S was signifi cantly (P<0.05)higher than the C for most of the experimental period (Figure 1; Table 1).The S showed higher mean Cu concentration than C for most part of the MINERAL STATUS IN TANZANIAN CROSSBRED DAIRY CATTLE experimental period (Figure 1).The overall mean Cu concentration of S was signifi cantly (P<0.001) higher than the C. The S had signifi cantly (P<0.001) higher mean MY and CBWT (P<0.01)than C (Table 1).

DISCUSSION
The mean plasma P concentration for the C was within a band of marginal defi ciency values, which is 3.1-4.7 mg/dl (Underwood and Suttle, 1999) while mean P concentration for S was above the values.The mean plasma Ca levels for both groups were within normal range of reference values, which is 9.6-12.3mg/ dl (Kaneko, 1989).The small variation in Ca values between the groups and the higher mean P values in S than C, could be due to the fact that Ca in serum is less responsive to dietary changes in intakes of the mineral than inorganic P (Betteridge, 1989) because of regulatory actions of parathyroid hormone, calcitonin and vitamin D, which in most species maintain the plasma concentration close to 10 mg/dl (Underwood and Suttle, 1999).Although the mean plasma Cu concentration of the S was higher than the C, both groups showed mean values within a marginal defi ciency band of values, which is 0.2-0.6 µg/ml (Underwood and Suttle, 1999).The present fi ndings suggest that the level of supplementation was not enough to raise the plasma Cu concentration to the recommended level or the availability of Cu was low.
The low mean MY for the C could be due to low energy intake among other factors.Low energy intake during late pregnancy can result in slightly lowered CBWTs and lower MY in the coming lactation (Cornelia and Barry, 2000).Low protein intake could also contribute to low MY since it decreases feed consumption, feed passage rates and overall digestive effi ciency (Cornelia and Barry, 2000).The P defi ciency could have contributed to the lower MY C compared to S, since animals respond to dietary defi ciency of P by reducing MY without affecting the P concentration in milk (Underwood and Suttle, 1999).
It is concluded that smallholder dairy cattle in Rungwe district suffer from P and Cu defi ciencies and that the increase of more than 0.5 kg in MY per kg supplement and a 10% increase in CBWT most likely could pay for the supplementation.

Figure 1 .
Figure 1.Plasma Ca, P and Cu concentrations trends between two months prepartum (C-2) and three months postpartum (C+3) for supplemented and control groups

Table 1 .
Least square means (LSMs ± Standard error) for selected minerals and production parameters