Effects of maternal age and offspring sex on milk yield, composition and calf growth of red deer (Cervus elaphus)

Abstract

Differential maternal allocation theory states that mothers will invest more heavily in the offspring sex that will secure higher reproductive output. Senescence theory is concerned with the gradual deterioration of physiological function with age. We analysed the offspring sex-dependent response of calf growth and milk traits to mother age in an Iberian population of captive red deer (Cervus elaphus) using a 22 year time series longitudinal data set. Previous studies revealed that there was little evidence for the differential allocation theory on milk traits and that most studies lacked proper control for confounding factors. Our results indicated that (i) calf growth was offspring male-biased, negatively affected by mother age and positively influenced by mother weight and parity, and (ii) there was no support for differential allocation offspring sex-dependence in milk traits (yield, energy density, fat, protein and lactose content). Our findings suggest that maternal allocation responds to offspring energy requirements, which are mainly driven by offspring body weight, and contingent on mother age and weight and previous maternal reproductive effort.

Figure 1

Prediction of male and female red deer calf weight against day of lactation contingent upon hind weight (a), hind age (b) and parity (c). Predictions are based on the model in Supplementary Information 3 Table 1 after fixing the main effects at their mean values and hind weight and hind age at their quartiles Q1, Q2 and Q3. (a) thin-magenta line: female calf; thick-black line: male calf; dotted, dashed and solid lines are 90 kg (Q1), 98 kg (Q2) and 107 kg (Q3) hinds body weight, respectively. (b) thin-magenta line: female calf; thick-black line: male calf; dotted, dashed and solid lines are hinds at age 3 years (Q1), 5 years (Q2) and 8 years (Q3) old. Triangle: male; circle: female.

Figure 2

Predictions of the response of milk constituents against red deer hind traits using models in Supplementary Information 3 Tables 2–5.

Figure 3

Predictions of the effect of red deer mother age on (a) milk yield (kg/d), (b) milk energy (MJ/kg), and (c) percentage of fat, (d) protein and (e) lactose in milk using models in Supplementary Information 3 Tables 2–6.