Visual assessment of body condition score (BCS) is used to aid individual cow and herd management, but the assessment is subjective and does not estimate actual body tissue reserves. Ultrasound (US) measurements of external fat reserves may be more objective. To quantify fat reserves at differing BCS`s, fat depth was measured by US on 87 mixed aged Friesian dairy cows on 6 occasions during a year. The US measurements were made at the 12th rib (RIB) and mid-way between the hip and pin bones (HIP). Animals were weighed (LW) and their BCS assessed visually at the same time. Mean BCS was greatest in early summer at 4.5 and lowest in late summer at 3.6. Mean RIB varied from 2.2 mm in mid spring to 3.6 mm in early winter, while mean HIP varied from 1.6 mm in early summer to 4.2 mm in early winter. Changes in BCS and LW were positively correlated. Age and growth in 2 year old animals did not appear to affect this relationship. BCS was positively correlated to both RIB and HIP fat depth. The correlation coefficient varied with time, being smallest in late summer (r = 0.37 & 0.26 for RIB & HIP respectively) and greatest in late lactation (r = 0.69 & 0.82 for RIB & HIP respectively). The ability of RIB & HIP measurements to predict BCS was low when BCS was <4.5, but predictability increased as fat depth and body condition increased. Cows at lower scores may deposit or deplete fat internally while having few external fat deposits. Because large changes in liveweight (LW) occurred without changes in BCS, or US, it is possible that fat deposits are internal or intramuscular rather than subcutaneous, and therefore not detectable from external inspection. Since most BCS values are <4.5 for lactating cows, the value of ultrasound to assess fat depots in lactating dairy cows is limited; however it may be of some value with cows of BCS >4.5.
Proceedings of the New Zealand Society of Animal Production, Volume 59, , 177-179, 1999
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