This experiment aimed to examine endocrine and metabolic responses to glucose, insulin, and adrenocorticotropin (ACTH) infusions in early-lactation dairy goats of different levels of milk production (LMP). Goats were grouped as either high (HY; 4.0 L/d, n = 13) or low milk yield (LY; 2.4 L/d, n = 13). Individual milk yield (L/d) and dry matter intake (DMI; kg/d) were measured daily. Concentration (mM) of glucose, fatty acids, and β-hydroxybutyrate, percent of milk fat and protein, body weight (BW; kg), and body condition score (BCS) were assessed weekly (from 2-6 wk postpartum). An intravenous glucose tolerance test (IVGTT), an insulin tolerance test (ITT), and an ACTH stimulation test were carried out at 43, 44, and 45 ± 0.7 d in milk, respectively. The HY goats had greater milk yield (+67%), energy-corrected milk (ECM; +70%), DMI (+28%), ratio of ECM output to metabolic BW (+67%), and feed efficiency (+25%), but lesser BCS than LY goats (2.4 vs. 2.6). The DMI (% of BW) was moderately correlated with ECM (r = 0.70) and negatively correlated with BCS (r = −0.57). At the time of the IVGTT, HY goats had lesser basal insulin and glucose than LY goats. However, results from IVGTT and ITT indicate that the sensitivity of peripheral tissues to insulin was unaffected by LMP. Compared with LY, HY goats had lesser insulin secretion (−52%) and greater insulin clearance rate (+47%) after glucose infusion. The ITT and ACTH stimulation test results show that both the growth hormone response to insulin and the cortisol response to ACTH were unaffected by LMP. Also, basal plasma concentrations of GH and cortisol were not correlated with glucose and fatty acids concentrations or any performance traits. Collectively, our results suggest that differences between HY and LY goats, concerning milk yield and feed efficiency, were probably more closely related to differences in insulin secretion and clearance than to differences in peripheral tissue responsiveness to the effects of catabolic and anabolic hormones.

The aim of this observational study was to identify the influence of key nongenetic factors such as month of kidding, parity, and litter size on milk yield and composition of Australian dairy goats throughout lactation. The study was conducted over 4 consecutive kidding seasons from June 2016 to March 2017. Data from 940 lactations of Saanen goats from a commercial herd were used to observe the effects of month of kidding, parity number, and litter size on total milk yield (L/goat) in early lactation (kidding to 90 d in milk; DIM), mid lactation (91-180 DIM), and late lactation (181-270 DIM), cumulative milk yield (from kidding to 270 DIM; CMY), average lactation length, proportion (%) of does reaching their target lactation length (270 DIM), somatic cell count (SCC), and percentages of milk fat and protein in early lactation. The mean herd responses throughout the entire study were as follows: CMY = 519 L/goat; lactation length = 233 d, with 70% of does reaching 270 DIM; milk fat = 4.2%; milk protein = 2.9%; and SCC = 6.2 × 10 5 cells/mL. Average milk production peaked in February and was lowest in June (2.4 vs. 1.8 L/goat per day, respectively). Milk yield was affected by month of kidding, parity number, and litter size in all phases of lactation. November kidders had the greatest CMY, and March kidders had the lowest CMY. March kidders had the shortest lactation length and the lowest proportion of does reaching 270 DIM. June kidders had the longest lactation length, whereas September kidders had the highest proportion of does reaching 270 DIM. Maximum milk yield was attained in third parity. Goats in fourth or greater parity had the shortest lactation length, the lowest proportion of does reaching 270 DIM, and the highest SCC. Goats delivering single kids had lower CMY, lower SCC, and higher percentages of fat and protein than does deliv-ering multiple kids. Our findings indicate that milk yield was primarily influenced by month of kidding, and the effects of month of kidding on milk yield were accentuated during mid lactation. However, the effects of month of kidding on milk yield varied significantly among parities.

The aim of this study was to evaluate temporal variations in circulating levels of selected hormones and metabolites in commercial dairy goats during the transition period. Blood samples from 940 goats were collected weekly, from −3 to 3 wk relative to delivery, to measure the effects of level of milk production, parity number, and litter size on concentrations of glucose, β-hydroxybutyrate (BHB), fatty acids, and plasma urea nitrogen (PUN). A subset of 80 goats [40 low-yielding (LY, < 1.8 L/d) and 40 high-yielding goats (HY, > 3.7 L/d)] were selected from the study population to measure the effects of level of milk production on plasma concentration of insulin, prolactin, and growth hormone. Average (±SD) milk yield (from 3 to 30 d in milk), body weight, and body condition score for the study population were 2.4 ± 0.78 L/d, 70 ± 16.0 kg, and 2.5 ± 0.28 units, respectively. Milk yield was moderately correlated with parity number (r = 0.49) but had weak correlation with litter size (r = 0.14). In multiparous but not in primiparous goats, antepartum concentrations of fatty acids and BHB increased with increasing litter size. Concentrations of fatty acids, BHB, and PUN were consistently lower in primiparous goats compared with those in second or greater parity. Postpartum, HY goats had higher ratios of glucose, fatty acids, and BHB to insulin than did LY goats, which might explain the greater mobilization of body tissues and enhanced milk production observed in this group. Collectively, our results indicate that increased milk yield has the most significant influence on the magnitude of body tissue mobilization. Our results also show that goats of higher parity display higher levels of lipid mobilization, and that both pregnancy and lactation are less able to elicit lipomobilization in primiparous compared with multiparous goats.

The objective of the present study was to use longitudinal data to examine the relationships between blood concentrations of nonesterified fatty acids (NEFA), β-hydroxybutyrate (BHB), and glucose during the transition period in dairy goats. Weekly blood samples were collected from Saanen goats from a commercial herd in Australia [1-7 yr; body weight 70 ± 16.0 kg; body condition score 2.5 ± 0.3; and daily milk yield 2.4 ± 0.73 L/d; all mean ± standard deviation (SD)]. The weekly prevalence of goats above hyperketonemic levels (BHB ≥0.8 mmol/L) was approximately 6 times greater postpartum than antepartum. As well, of the 935 goats sampled antepartum, 50 (5%) had at least 1 hyperketonemic event, and 823 (88%) had at least 1 event of NEFA above the threshold (≥0.3 mmol/L). Of 847 goats tested postpartum, 258 (30%) had at least 1 hyperketonemic event, and 690 goats (81%) had at least 1 event of NEFA above the threshold (≥ 0.7 mmol/L). Substantial variation was found when analyzing the mean days of maximum NEFA and maximum BHB concentrations antepartum (−11 ± 6.6 and −14 ± 7.2 d, respectively, mean ± SD) and postpartum (14 ± 6.6 and 9 ± 6.8 d, respectively, mean ± SD). We observed moderate to strong relationships between NEFA and BHB concentrations (r = 0.66) and between NEFA and glucose concentrations (r = −0.46) throughout the transition period. Our results suggested that 3 to 16 d in milk is the best sampling window for monitoring hyperketonemia in dairy goats, and that results from simultaneous BHB and glucose tests provide an improved indication of the fat mobilization and energy status of the herd when measured close to this timeframe.

This experiment aimed to examine the association between surrogate indices of insulin resistance (IR)-namely, the homeostasis model of IR (HOMA-IR), quantitative insulin sensitivity check index (QUICKI), and revised quantitative insulin sensitivity check index (RQUICKI)-and measures of IR obtained from an intravenous glucose tolerance test (IVGTT) performed in early-lactation dairy goats. Despite a moderately strong correlation between surrogate indices of IR and insulin area under the curve, we found no significant relationship between surrogate indices and measures of reduced insulin sensitivity, such as glucose clearance rate, glucose area under the curve, and insulin sensitivity index. Thus, our results suggest that surrogate indices of IR are not suitable for assessing the insulin sensitivity of peripheral tissue in early-lactation goats. Highlights• There was no correlation between surrogate indices of IR and measures of insulin sensitivity derived from the IVGTT. • Surrogate indices were moderately correlated with measures of insulin secretion.• Surrogate indices of IR are not indicated for assessing peripheral tissue insulin sensitivity in early-lactation goats.

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Evidence suggests that camel milk (CM) can have insulin-like actions, although the mode of action is not understood. Using the pig as a monogastric model, this pilot experiment examined the effects of CM consumption on metabolic responses to an in vitro glucose tolerance test (IVGTT). Twenty female Large White x Landrace pigs were individually housed for 6 wks and randomly allocated to one of the following four diets (fed ad libitum; n = 5): control (Con); high fat (HF; ~16% fat); raw CM (the HF diet plus 500 mL CM/ day); or pasteurized CM (PCM). Blood samples were collected on two occasions (weeks 2 and 5). At week 6, the pigs were fitted with an ear vein cannula and the following day an in vitro glucose tolerance test (IVGTT) was conducted (0.3 g/kg BW glucose). Plasma fatty acids and cholesterol concentrations were greater in the pigs fed the HF diet and greatest in those fed CM, while there was no effect of diet on insulin concentrations. The pigs fed CM tended to have a reduced peak insulin (p = 0.058) and an increased glucose nadir (p = 0.009) in response to the IVGTT. These preliminary results tend to support the hypothesis that feeding CM can improve glycemic control in pigs.

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