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

[摘要] English: An investigation was launched to determine the influence of the P status of grazing beefcattle on their production and reproduction on the veld of Saratoga in the NorthwestProvince. The study at this site dealt with the following aspects:topographical, climatic and nutritional factors which might have had aninfluence on the study;the lick intake and the effects of P supplementation on the productiveperformance of beef cows;the effect of P supplementation on the reproductive performance of beefcows and calf performance; andrib bone and blood as indicators of the P status of the reproducing beefcows.The main treatments (+P and -P) basically comprised 60 beef cattle type cows. Thesecows were divided in two separate groups of 30 each. The +P cows were supplementedwith 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 andquality of vegetation ranged from average to poor at the site. The lick intake wasextremely high with the start of the trial at Saratoga. The intake of the +P treatment grouplater decreased to the acceptable level of 80 g NaC1 - and 6 g P/cow/day but the -Ptreatment group was still maintaining a high salt lick intake.The production of the cows, in the +P treatment over the trial period at Saratoga wassignificantly (P < 0.05) better compared to the -P treatment cows. The +P cowsachievement in terms of the growth of their calves was in general better compared to thecalves of the -P cows. However, there was no difference in terms of reproductionbetween the treatments during the whole period of the trial. When considering allmeasured 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 certainamount 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 afterthe trial commenced. The -P cows very rapidly developed clinical symptoms, notablystiffness, anorexia and discoordination, followed with deaths a few months after the trialstarted. At this stage (weaning) the -P cows averaged only 112.1 mg P/cm3, which is asignificantly (P < 0.05) lower P content of fresh bone compared with the +P cows (124.4mg 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 periodshowed 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 theMolopo. Although, the results of the trial led to the hypothesis that an excessive intake ofNaCI may induce a P deficiency in ruminants, as could have been the case in the -Ptreatment group at Saratoga, no clear answers were provided by the trial during the firstphase of investigation. According to the results further and more detailed research isneeded, concerning not only P but NaCI as well. However, in the interim it must beaccepted that the cows suffered from a P deficiency when not supplemented with P on theveld and it will be wise to provide some P especially when extreme drought conditionsprevail.

[发布机构] University of the Free State