Influence of Temperament on Skeletal Muscle Mitochondrial Capacity of Brahman Cows

To investigate a potential relationship between animal temperament and mitochondrial function, 5-yr-old Brahman cows were stratified into one of three temperament groups based on herdsman scores: T1 (n=4; calm), T2 (n=4; normal), or T3 (n=4; temperamental). The cows were processed at the departmental meats lab and samples from the longissimus dorsi (LD) and semitendinous muscles were collected. All samples were assessed for mitochondrial density (via citrate synthase activity) and function (via cytochrome c oxidase activity); samples from the LD were also evaluated for mitochondrial capacity utilizing high-resolution respirometry. Data were analyzed using the MIXED procedure of SAS (9.4). Relative to mg of tissue (integrative mitochondrial capacity), temperamental cattle (T3) had greater state 3 oxidative phosphorylation capacity with complex I substrates (P_CI), P_CI plus complex II substrates (P_CI+II), maximum electron transport capacity (E_CI+II), and E_CII than T1 (P=0.009, P=0.03, P=0.02, and P=0.04 for P_CI, P_CI+II, E_CI+II, and E_CII, respectively) or T2 (P=0.03, P=0.02, P=0.03, and P=0.03 for P_CI, P_CI+II, E_CI+II, and E_CII, respectively). Temperamental cattle (T3) also had a higher fractional control ratio of P_CI+II (0.890 ± 0.023) than T2 (0.780 ± 0.025; P=0.02), with T1 being intermediate (0.814 ± 0.023). This indicates a greater contribution of complex II to oxidative phosphorylation and energy production in temperamental animals, the effects of which are unknown at this time. Temperamental animals (T3) also had the greatest citrate synthase activity across muscle groups (9.49 ± 0.70 nmol/min*mg tissue) compared to T1 (6.44 ± 0.68; P = 0.009) or T2 (5.29 ± 0.59; P = 0.0008), indicating greater skeletal muscle mitochondrial density in T3. Intrinsic mitochondrial capacity (relative to CS activity) and cytochrome c oxidase activity (mitochondrial function) were not different between muscles, nor between temperament groups. Research is needed to clarify the significance of different patterns of energy production in temperamental cattle. Further, skeletal muscle mitochondrial capacity may be a useful early indicator of animal performance and carcass quality at harvest.

Table 1. High-resolution respirometry data from longissimus dorsi muscles between calm (T1), normal (T2), and temperamental (T3) Brahman cows.

O2Flux (pmol/s*mg tissue)1	T1	T2	T3	SEM	P-value
PCI	14.92	14.50	21.97	0.41	0.037
PCI+II	19.35	18.73	31.01	2.65	0.039
ECI+II	23.70	24.09	34.69	2.44	0.042
ECII	13.54	12.81	22.19	2.23	0.056

¹P = state 3 oxidative phosphorylation; _CI = pyruvate + malate + glutamate; _CI+II = pyruvate + malate + glutamate + succinate; E = electron transport system capacity.