A Comparison of Three Strains of White Clover

Abstract

During the past few years much publicity has been given to the losses caused by bloat in cattle, and the suggestion has been made that the incidence of bloat has increased owing to the use in leys ofthe white clover S.IOO. To investigate this, observations on tendency to bloat were made on a series of experimental plots of S.IOO, S.IOO Nomark and S.184 white clovers, each sown in association with S.23 perennial ryegrass. The observations included a study of factors influencing the occurrence of bloat as well as its incidence relative to each of these three strains. Details of the experimental plots and of the herbage yield and botanical composition of each of the swards at the time of grazing have been described and discussed in Part I.The definition of bloat adopted in this paper is the retention of gas in the rumen ofthe animal in excess of normal amounts. This definition is wider than that employed by veterinarians,ŵ hich relates mainly to those cases of rumen distension likely to result in the death ofthe animal. Bloat in its less acute form may, however, considerably retard growth and development through its general effect on the animal's health. One ofthe essential conditions ofthe efficient production of meat or milk is the absence of digestive disturbances in the animal. It was thought, therefore, that the less serious cases should also be studied, and for this reason note was taken of all degrees of bloat. EXPERIMENTAL PROCEDUREThe experimental grazing of the plots was controlled in a manner designed to secure a good growth of grass each time the plots were grazed, so as to create as far as possible the most favourable condition for the development of bloat. The plots were grazed by Welsh Black cattle three times each season, in May, June and August, during each of three harvest years 1949 to 1951. As insufficient stock was available to graze all the plots at once, a block containing a single plot of each ofthe three seeds mixtures was grazed at a time, followed by other blocks in sequence. There were four replicate blocks, making a total of twelve plots. Each plot within the block was separately fenced and was grazed by a different group of animals. There was a large variation between the animals in their tendency to bloat, and an attempt was made to reduce the influence of this individuality to a minimum by ensuring that each animal was transferred to a different seeds mixture plot when moved from one replicate block to the next. As there were four blocks, but only three seeds mixtures, it was inevitable that each animal should graze one seeds mixture twice. For the purpose of comparisons involving the three clover strains, only the marks for bloat recorded when an animal was grazing a plot of a particular white clover strain for the first time at each grazing period were considered.The actual number of animals placed on a plot depended upon the amount of herbage available, and the stocking was generally such that all of it was consumed in 3-4 days. At the end of this period there was little left, so t...

Observations on the etiology, prophylaxis and therapy of pasture bloat

“…(1957) found no effects due to climate in their bloat trials. Troughton (1955) found no correlations between maximum and minimum temperatures, rainfall, sunshine, or humidity and the incidence of bloat. Barrentine (1959) found no basis for the belief that grazing dew-or rain-wet legumes causes bloat and suggested that most cases of critical bloat actually occur on clear warm days.…”

“…On the other hand, Troughton (1955) extrapolates from the work of another investigator with sudan grass in suggesting that increases of bloat noted on plots low in soil phosphate may have resulted from increased cyanide content of the clover forage consumed. Total intake of cyanide was correlated with bloat incidence.…”

“…Troughton (1955) found that most bloat occurred during the first 24 hours animals grazed a given plot.…”

“…(1956b), Johns (1954), andHan cock (1954) all found that such was definitely not the case, and Huffman and Cole ) review several papers in which bloat incidence and severity were reported to be in dependent of total intake or rate of intake. Troughton (1955), however, suggests that intake may be correlated with bloat.…”

“…He found that both phosphorus and potassium were necessary for optimal yields. Troughton (1955) On the other hand, Ward (1959) reports that phosphorus fertilization did not prevent bloat while Barrentine (1959) found evidence that high phosphorus levels aggravated bloat. Power et_ al.…”