Phosphorus supplementation to grazing beef cows in the Molopo region (Saratoga) of the North-West Province

English: An investigation was launched to determine the influence of the P status of grazing beef cattle on their production and reproduction on the veld of Saratoga in the Northwest Province. The study at this site dealt with the following aspects: topographical, climatic and nutritional factors which might have had an influence on the study; the lick intake and the effects of P supplementation on the productive performance of beef cows; the effect of P supplementation on the reproductive performance of beef cows and calf performance; and rib bone and blood as indicators of the P status of the reproducing beef cows. The main treatments (+P and -P) basically comprised 60 beef cattle type cows. These cows were divided in two separate groups of 30 each. The +P cows were supplemented with P and salt in a lick, while the -P cows received only a salt lick. An extremely poor rainfall during a very dry 1992, had the effect that the quantity and quality of vegetation ranged from average to poor at the site. The lick intake was extremely high with the start of the trial at Saratoga. The intake of the +P treatment group later decreased to the acceptable level of 80 g NaC1 - and 6 g P/cow/day but the -P treatment group was still maintaining a high salt lick intake. The production of the cows, in the +P treatment over the trial period at Saratoga was significantly (P < 0.05) better compared to the -P treatment cows. The +P cows achievement in terms of the growth of their calves was in general better compared to the calves of the -P cows. However, there was no difference in terms of reproduction between the treatments during the whole period of the trial. When considering all measured variables, the -P cows realised the poorest performance in the trial at Saratoga. The results suggested that the -P cows could not produce without receiving a certain amount of supplementary P in their diet, especially when drought conditions prevailed. At Saratoga there was a rapid loss of weight of the cows in both treatments shortly after the trial commenced. The -P cows very rapidly developed clinical symptoms, notably stiffness, anorexia and discoordination, followed with deaths a few months after the trial started. At this stage (weaning) the -P cows averaged only 112.1 mg P/cm3, which is a significantly (P < 0.05) lower P content of fresh bone compared with the +P cows (124.4 mg P/cm3). This is thus an indication of a P deficiency, as we assured at this stage (weaning). However, the average of the P content of fresh bone over the trial period showed no indication of a P deficiency between the two treatments. The purpose of this study was to determine if a P deficiency exists at Saratoga in the Molopo. Although, the results of the trial led to the hypothesis that an excessive intake of NaCI may induce a P deficiency in ruminants, as could have been the case in the -P treatment group at Saratoga, no clear answers were provided by the trial during the first phase of investigation. According to the results further and more detailed research is needed, concerning not only P but NaCI as well. However, in the interim it must be accepted that the cows suffered from a P deficiency when not supplemented with P on the veld and it will be wise to provide some P especially when extreme drought conditions prevail.