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GRAZING PATTERN OF DAIRY COWS THAT WERE SELECTED FOR DIVERGENT RESIDUAL FEED INTAKE AS CALVES

Discipline: grazing/pastures; Key words: dairy cow, residual feed intake, grazing behavior

 

I have previously reported on the topic of residual feed intake (RFI) or net feed intake as selection criterion for feed efficiency in dairy cows. The subject also received attention at the June 2015 Large Herd Conference, showing promising results. Research across the globe suggests improvement in efficiency of feed utilization, immunity and therefore  resistance to disease and infections, longevity and fecundity, and lower methane production in cows with lower RFI (less feed intake in relation to energy requirements for a given milk yield). Recently, other and surprising results have come to the fore; one study being with grazing cows and therefore with relevance to our pasture-based systems. The study was conducted by Dr P. Gregorini and co-workers and reported in The Journal of Dairy Science, Volume 98 (Issue 9) of 2015, pages 6486 to 6491, with the title: Grazing pattern of dairy cows that were selected for divergent residual feed intake as calves.

The aim of this study was to investigate and assess differences in the grazing pattern of two groups of mature dairy cows selected as calves for divergent RFI. Sixteen Holstein-Friesian cows (470 kg body weight and 100 days in milk), comprising eight cows selected as calves for low (most efficient: CSCLowRFI) and eight cows selected as calves for high (least efficient: CSCHighRFI) RFI, were used in the study. The cows were managed as a single group, and strip-grazed (24-hour pasture allocation at 0800 hour) a perennial ryegrass sward for 31 days, with measurements taken during the last 21 days. All cows were equipped with motion sensors for the duration of the study, and jaw movements were measured for three 24-hour periods during three random but non-consecutive days. Measurements included number of steps and jaw movements during grazing and rumination, plus faecal particle size distribution. Jaw movements were analyzed to identify bites, mastication (oral processing of the material eaten) during grazing bouts, chewing during rumination, and to calculate grazing and rumination times for 24-hour periods. Grazing and walking behaviour were also analyzed in relation to the first meal of the day after the new pasture was allocated.            

The cows selected for low RFI (CSCLowRFI) as calves appeared to (a) prioritize grazing and rumination over idling; (b) take fewer steps, but with a higher proportion of grazing steps at the expense of non-grazing steps; and (c) increase the duration of the first meal and commenced their second meal earlier than CSCHighRFI. The CSCLowRFI had fewer jaw movements during eating (39,820 versus 45,120 for CSCLowRFI and CSCHighRFI, respectively), more intense rumination (about five more chews per bolus), and their faeces had 30% less large particles than CSCHighRFI. These results suggest that CSCLowRFI concentrate their grazing activity to the time when fresh pasture is allocated, and graze more efficiently by walking and masticating less, hence they are more efficient grazers than CSCHighRFI.