Studies in grazing behaviour of dairy cattle: II. Bloat in relation to grazing behaviour

Abstract

1. Four trials on methods of bloat-prevention vare described: (a) A comparison of ‘break’ grazing and normal ‘rotational’ grazing without restriction of feed in either case. Break grazing observations covered two and five breaks per day.(b) A comparison of these two systems where ‘break’ grazing involved restriction of area available to the cows, and ‘breaks’ varied from seven to eleven per day.(c) Comparison of ‘off and on’ grazing with normal rotational methods in an attempt to force changes in grazing pattern.(d) Comparison of the same pasture grazed at different lengths under rotational grazing methods.2. Grazing behaviour and degree of bloat were noted.3. In general, the results showed that, irrespective of number of breaks, break grazing with or without restriction gave no effective control of bloat.4. There were definite indications that a strictly enforced system of ‘off and on’ grazing could afford considerable practical control.5. Long feed proved definitely safer than feed of the same botanical composition grazed at shorter stages of growth.6. It was found that cows on potentially dangerous grass had short grazing times with few periods of intense activity. Thus, the oft-stated opinion that bloat is caused by cows eating greedily of dangerous pastures was not substantiated. On the contrary, cows on such pasture showed marked reluctance in their grazing activity.7. Bloat-producing swards were also associated with reduced rumination time, even in respect to cows showing no symptoms. Bloated cows showed generally very low rumination times.8. Many of these observations were made on identical twins. From the similarity in their behaviour, it can be concluded that inheritance is an important factor affecting the occurrence of bloat amongst cows grazing the same herbage.9. In the early stages of bloat, ruminal movement and belching increased in frequency and intensity. This is contrary to the theory that bloat is due to rumen atony. Atony was observed only in the advanced stages of the trouble.

Effect of time of grazing or cutting and feeding on the incidence of alfalfa bloat in cattle

“…However, there has been little formal experimentation on the effect of feeding schedule on the incidence of bloat. We are not aware ofany published reports between 1954 (Hancock 1954) and1990 (Hall and Majak 1990). In the latter study we found that animals fed freshly harvested alfalfa twice a day (30 kg at 0830 h, 20 kg at 1400 h) bloated more than when they were offered the same total amount of feed once a day at 0830 h. When bloat occurred, it was observed only after the morning feeding.…”

Bloat in cattle grazing alfalfa cultivars selected for a low initial rate of digestion: A review

“…Eructation and feeding behaviours are modified as the rumen's static pressure increases, to adjust to the new gas dynamics (Cole et al 1945). Grazing bouts are shorter, rumination times are reduced and ruminal movements increase in frequency (Hancock 1954). Production losses are primarily a result of a reduced feed intake (Johns 1954;Reid and Johns 1957;Alder et al 1967;Hall et al 1988).…”

“…Input and output from the rumen can be indirectly affected by adopting grazing and feeding regimens that increase rumen clearance, or reduce gas and foam production. Control is a function of the rancher's skill at managing the interaction between availability and digestibility of pastured forage and the grazing behaviour of the animals (Hancock 1954;Allison 1985;Hall et al 1994b;Majak et al 1995).…”

Observations on the etiology, prophylaxis and therapy of pasture bloat

“…The importance of heredity in accounting for variations in individual susceptibility has been reported in papers re viewed by Huffman , in identical twin studies conducted by Hancock (1954) and by Johns (1954) and other studies reviewed by Johns (1956a). Some mechanisms prob ably affected by heredity and related to bloat are differences in composition of the saliva , differences in the efficiency of eructation (Huffman, in Cole et.…”

“…Alteration of the grazing, pattern Hancock's (1954) trials with identical twins are classics in this area. He found that strip grazing, with or without restrictions of in take, gave no effective control of bloat.…”