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Relationships between longissimus dorsi muscle depth, body weight, and parity during the first five months of lactation.

C. J. McCabe

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06-22-2020

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Abstract:

M102
Relationships between longissimus dorsi muscle depth, body weight, and parity during the first five months of lactation.
C. J. McCabe*, J. P. Boerman. Purdue University, Department of Animal Sciences West Lafayette, IN.

Due to insufficient dry matter intake and heightened nutrient demands in the first weeks of lactation, cows mobilize their own muscle and adipose tissue to bridge these nutrient gaps. The objective of this study was to analyze changes in muscle depth and BW in primiparous and multiparous animals from early through mid-lactation. Holstein dairy cows (n = 38; 1st lactation n = 14, 2nd+ lactation n = 24) were weighed and their muscle depth was measured 1x per month following the morning milking for 5 mo to quantify BW and muscle depth changes from early through mid-lactation. We captured muscle depth images from the right side of each cow from the 12th intercostal space of the longissimus dorsi muscle using an ALOKA SSD-500 ultrasound with a linear transducer. At each time point, 3 images were captured, and an average was quantified using ImageJ software (NIH; Bethesda, MD). There were no differences in longissimus dorsi muscle depth between primiparous and multiparous cows (P = 0.77). However, BW was higher for multiparous dairy cows (577 vs. 691 kg; P < 0.0001) compared with primiparous cows. Muscle depth was lower for the second month of lactation (4.07 cm) compared with the fourth month of lactation (4.42 cm; P < 0.05). Measurements taken over the study for muscle depth and BW were positively correlated (r = 0.35; P < 0.0001). Change in BW and change in muscle depth in the first month were positively correlated (r = 0.83; P < 0.0001). Extent of both BW and muscle depth loss in the first month was negatively correlated with BW change in the second month (r = −0.66 and r = −0.59; P < 0.05, respectively). Likewise, muscle depth change from in the second month of lactation was negatively correlated with muscle depth change in the third month (r = −0.88; P < 0.0003). A considerable amount of BW, specifically muscle, is mobilized during the first 2 mo of lactation with more accretion of muscle starting in the third month of lactation. Understanding the timing and extent of muscle mobilization and accretion will allow us to meet nutrient requirements of lactating dairy cows.

Keywords: ultrasound, muscle depth, parity.