Successful transfer of passive immunity: the natural alternative to antibiotics for boosting the survival of intensively reared dairy goat kids.

In dairy operations, antibiotics have traditionally been used to treat, prevent, and control diseases. However, given the mounting global crisis of antimicrobial resistance (AMR), farmers are urged to re-assess and reduce their reliance on antibiotics. Thus, this randomized, double-blinded cohort study aimed to estimate the prevalence of failed and successful transfer of passive immunity (FTPI and STPI) in dairy goat kids reared under commercial conditions, and the effects of antibiotic metaphylaxis on the pre-weaning (≤42 d old) mortality in FTPI and STPI kids. Plasma concentration of immunoglobulin G at 1d old (pIgG-24 h) was measured in 747 male Saanen kids for the determination of FTPI and STPI (pIgG-24 h < 12 and ≥12 g/L, respectively). Kids were then randomly divided into two groups: those receiving a single penicillin injection at 1 d old (PEN), and those receiving no treatment (CTR). The mean (±SD) pIgG-24 h and initial BW (IBW) were 17 ± 9.8 g/L and 4.1 ± 0.64 kg. The prevalence of FTPI was 29% (220/747 kids). Gastrointestinal complications were the primary cause of death (41%), followed by septicemia (22%) and arthritis (17%). A single penicillin injection reduced preweaning mortality by 55% (10 vs 22%, PEN vs CTR). However, results suggest that such a decline was mainly driven by the improved survival rates among FTPI kids, which increased by 19% (from 62% in CTR-FTPI to 82% in PEN-FTPI), as opposed to an 8% increase among STPI kids (from 85% in CTR-STPI to 93% in PEN-STPI). Additionally, the odds of mortality ≤ 42 d old were threefold higher in the CTR-FTPI group when compared to both the CTR-STPI and PEN-FTPI groups, suggesting a potential parity between STPI and PEN for mortality rate reduction. Taken together, the results indicate that although metaphylactic antibiotics can halve preweaning mortality, similar improvements are likely to be achieved via increased STPI rates. Furthermore, by targeting metaphylactic interventions to high-risk groups (i.e., those displaying signs of inadequate colostrum intake and/or low birth BW), farmers could reduce treatment costs and mitigate AMR risks. While these findings carry considerable weight for commercial dairy goat practices, their applicability to other systems (i.e., extensive, semi-intensive, mohair, meat systems) warrants further investigation.

Evaluation of plasma immunoglobulin G and BW thresholds for predicting preweaning mortality in commercially raised dairy goat kids.

The high preweaning mortality rate is a concerning issue for the commercial dairy industry. In this context, early identification of at-risk individuals can be instrumental. To address this, we conducted a prospective cohort study with the objective of evaluating plasma immunoglobulin G concentration (pIgG-24 h) and initial BW (IBW) measured at 1d old in 363 male dairy kids (Saanen) for predicting preweaning mortality under commercial conditions. Receiver operator characteristic (ROC) analysis was used to determine critical thresholds for pIgG-24 h and IBW. Subsequently, areas under the curve (AUC), sensitivity (Se), and specificity (Sp) were examined to assess the accuracy of these thresholds. Multivariable regressions were used to model odds ratios (OR) for mortality, controlling for confounding effects between IBW and pIgG-24 h. The mean (±SD) pIgG-24 h and IBW were 16.4 ± 9.37 g/L and 4.0 ± 0.61 kg. Overall mortality ≤ 14d and ≤42d old was 12% and 21%, respectively. Critical pIgG-24 h thresholds predicting mortality ≤ 14 d and ≤42 d old were < 10.1 g/L (AUC = 0.74, Se = 59%, and Sp = 82%) and <11.4 g/L (AUC 0.70, Se = 53%, and Sp = 77%), respectively. Kids with pIgG-24 h < 10.1 g/L were six times more likely to die ≤ 14 d old [OR; 95% CI (6; 3-12)], and kids with pIgG-24 h < 11.4 g/L were four times more likely to die ≤ 42 d old (4; 2-6). The IBW threshold most linked to mortality ≤ 14 d was <3.95 kg (AUC 0.60, Se = 59%, and Sp = 61%). However, this association became inconclusive after adjusting for pIgG-24 h differences. Conversely, an IBW of <3.0 kg was associated with notably higher mortality odds within both 14 and 42 d, irrespective of pIgG-24 h levels (10; 3-37, and 4; 1-20, respectively), suggesting that kids with an IBW < 3.0 kg face an increased likelihood of dying before 42 d, irrespectively of their IgG levels. While our findings suggest pIgG-24 h < 11.4 g/L and IBW < 3.0 kg as strong indicators of early mortality risks in male dairy kids, these results require further validation for other systems.

Comparison of measures of insulin sensitivity in early-lactation dairy goats.

This experiment aimed to investigate the correlations between surrogate indices of insulin resistance (IR)-namely, the homeostasis model of IR, the quantitative insulin sensitivity check index, and the revised quantitative insulin sensitivity check index-and measures of IR obtained from an intravenous glucose tolerance test (IVGTT) performed in early-lactation dairy goats. Saanen goats (n = 26) with varying levels of milk production (1.7-4.8 kg/d) were selected and underwent an IVGTT on 43 ± 0.7 d postpartum (mean ± standard deviation). Data from the IVGTT were fitted in the minimal model to calculate parameters of glucose-insulin dynamics such as insulin sensitivity index and acute insulin response to glucose. Surrogate indices were computed using the average of the IVGTT basal samples. Correlation analysis revealed no relationship between surrogate indices of IR and measures of IR derived from the IVGTT (e.g., insulin sensitivity index, glucose clearance rate, glucose area under the curve). Therefore, our results suggest that surrogate indices of IR are not suitable for assessing the insulin sensitivity of peripheral tissue in early-lactation goats.

An Extended Photoperiod Increases Milk Yield and Decreases Ovulatory Activity in Dairy Goats.

Short day length is associated with reduced milk production in dairy ruminants. Dairy ruminants have been kept in lit sheds during winter to extend the day length and stimulate milk production. However, there studies are few on the effect of an extended photoperiod on the ensuing reproductive performance of dairy goats. The aim of this study was to examine the effect of long day photoperiod (LDPP) and exposure to bucks on milk production and plasma progesterone and prolactin in dairy goats. The study was conducted in 122 non-pregnant lactating dairy goats over 18 weeks from April to August (late autumn and winter in the Southern Hemisphere). The goats were kept in open sided sheds in which the control treatment received ambient lighting while the LDPP treatment received 16 h of light, including artificial lighting. In June, July and August synchronised does were randomly assigned each month to the presence or absence of a buck and ovulatory activity determined from plasma progesterone. Plasma progesterone concentrations were reduced (0.73 vs. 0.46 pmol, p < 0.001) while prolactin concentrations were increased (0.095 vs. 1.33 ng/mL, p < 0.001) in LDPP goats. The former response was most marked in late winter (0.58 vs. 0.004 pmol, p < 0.001) indicating a lack of functional corpora lutea. While there was no overall effect of buck exposure on plasma progesterone concentrations there was a three-way interaction such that plasma progesterone concentrations were increased (p < 0.05) by exposure to bucks in LDPP goats in August (late winter) but not at other times. Milk production was increased in LDPP goats over the latter stages of the study (1. 55 vs. 1.82 L/d, p < 0.05). Also, persistency of lactation was greater in LDPP goats with fewer goats drying off (13 vs. 0%, p < 0.05). These findings suggest that LDPP can increase milk production and persistence while decreasing ovulatory activity in dairy goats.

Endocrine and metabolic responses to glucose, insulin, and adrenocorticotropin infusions in early-lactation dairy goats of high and low milk yield.

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 ß-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.

Short communication: Associations between nonesterified fatty acids, ß-hydroxybutyrate, and glucose in periparturient dairy goats.

The objective of the present study was to use longitudinal data to examine the relationships between blood concentrations of nonesterified fatty acids (NEFA), ß-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.

Endocrine and metabolic status of commercial dairy goats during the transition period.

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, ß-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.

Effects of month of kidding, parity number, and litter size on milk yield of commercial dairy goats in Australia.

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 × 105 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 delivering 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.

Artificial lighting during winter increases milk yield in dairy ewes.

In Australia, the supply of sheep milk is reduced during the winter. Housing dairy animals under lights during winter is a simple technique to increase milk yield; however, it is difficult to predict the magnitude of this increase in dairy ewes, because there are few corroborating data. We studied 220 East Friesian crossbred ewes (50 primiparous and 170 multiparous ewes, respectively) that lambed in April to May 2007 (late autumn, southern hemisphere) and were weaned from their lambs within 24 h of parturition and milked exclusively by machine. These ewes were ranked according to their milk production, and ewes producing > or =1,000 mL/d of milk were allocated to 1 of 2 groups. One group of ewes was kept indoors under a long-day photoperiod (16 h of light), whereas the other group was kept indoors under a naturally declining day length. Ewes were maintained under these conditions for 8 wk. Milk yield was measured twice weekly, and ewe weight and condition were measured at weekly intervals. From a subset of ewes (n = 20 per group), milk samples were collected twice weekly at the morning milking to measure milk lipid, protein, and lactose, and blood samples were collected once a week to measure plasma prolactin concentrations. Mean daily milk yield was analyzed as a percentage of preexperimental milk yield because the milk yield of ewes housed under the long photoperiod was lower than that of ewes under a declining day length when the treatments began. Thus, the ewes under a long photoperiod yielded 91.7% of their starting yield by wk 8 of treatment, whereas ewes under a declining day length yielded 76.25% of their initial value (LSD = 5.1), and this divergence in milk yield was apparent by wk 2 of treatment. Mean plasma prolactin levels were greater in ewes housed under the long-day photoperiod (n = 20) compared with control ewes (n = 20) at wk 6 (168 +/- 27 vs. 72 +/- 19 ng/mL, respectively), wk 7 (125 +/- 28 vs. 37 +/- 7 ng/mL, respectively), and wk 8 of the experiment (132 +/- 35 vs. 31 +/- 7 ng/mL, respectively). The composition of the milk was similar between the groups at each time point, and milk from these ewes (n = 20 per group) contained, on average, 6.1 +/- 0.05% lipid, 4.8 +/- 0.02% protein, and 5.4 +/- 0.01% lactose (n = 309 samples). We concluded that ewes increase milk production in response to being housed under a long-day photoperiod during winter.

Predicting milk yield in sheep used for dairying in Australia.

It is necessary to identify traits that are simple to measure and correlated with milk yield to select ewes for dairying from existing populations of sheep in Australia. We studied 217 primiparous and 113 multiparous (second parity, n = 51; third parity, n = 40; and fourth parity, n = 22) East Friesian crossbred ewes, for 2 consecutive lactations, that were milked by machine following a period of suckling (24 to 28 d). We measured lamb growth, milk production, milk yield, and residual milk during early lactation (