Influence of oestrus on the heat stability and other characteristics of milk from dairy goats

Effect of stress on somatic cell count and milk yield and composition in goats

There is little information about the effect of the stress on Somatic Cell Count (SCC) and milk yield and composition in goats. A total of 40 goats in their 4th month of lactation were assigned to two groups: stress (STR) and untreated (CON). Goats of STR were exposed to acute stress (visual and auditory stimulus from a barking dog for 20 min on day 0). After the stress, average values of plasma cortisol were higher in STR than CON (P < 0.001); likewise, in STR group cortisol was lower in parity 1 + 2 goats than parity ≥3 goats (P < 0.05). Stress caused a considerable increase in SCC in parity ≥3 goats (P < 0.05), but not in parity 1 + 2 goats. On average, this increase of SCC was 6-fold compared to values prior to the stress, and it was observed in both healthy and infected mammary glands. This increase was transient, as SCC returned to normal values after 1 to 3 days. On day 1, stressed goats of parity ≥3 produced 11% less milk compared with day 0 and, regarding milk composition, only lactose showed a significant drop. Stressed parity 1 + 2 goats showed no changes in SCC and milk yield and composition. We conclude that, in goats, stress is a non-infectious factor that can interfere in the use of SCC as an indirect method of intramammary infection (IMI) detection or, in bulk tank milk, as a commercial milk quality parameter.

Effect of steroid hormones on the innate immune response induced by Staphylococcus aureus in the goat mammary gland

The objective of this study was to compare the dynamics of innate immune components after intramammary infusion of Staphylococcus aureus (SA) under conditions of high oestrogen and high progesterone in goats. In one group ("E-group"), controlled internal drug release (CIDR) devices were inserted intravaginally from days -11 to -4. Prostaglandin F2α was administered immediately after removal of the CIDR device at day -3, and then oestradiol benzoate (E) was injected intramuscularly once a day from days -2 to 3. Heat-inactivated SA was then administered via intramammary infusion to the left udder at day 0, whilst only saline was infused to the right udder as a control. In a second group ("P-group"), CIDR devices were inserted intravaginally from days -3 to 7 and SA was infused at day 0 in the same way as in the E-group. The milk yield and the concentration of innate immune components (somatic cell count (SCC), lactoferrin (LF), S100A7 and goat ß-defensin 1 (GBD-1)) in the milk were measured. Milk yield decreased drastically in both SA and control udders in the E-group, whereas the P-group exhibited increased milk yield in both SA and control udders. SCC increased after SA infusion in both E- and P-groups, although it was higher in the E-group than in the P-group. There was no significant change in LF concentration in the E-group, but a decrease was observed in the P-group. Concentrations of S100A and GBD-1 were significantly increased after SA infusion in the E-group but not in the P-group. These results suggest that E enhances the innate immune response induced by SA in the goat mammary gland. This effect may be due to the reduction in milk yield and upregulation of innate immune components.

Effect of intramammary infection on milk electrical conductivity in Murciano-Granadina goats

Measurements of electrical conductivity (EC) of milk are used in mastitis detection in cows due to the low cost, possibility of automation, and rapid diagnosis, but the literature about EC measurement in goats is scarce. In this study, we studied the effect of the establishment of intramammary infection (IMI) on EC of goat milk by gland using daily measurements. Additionally, the effects on milk yield, somatic cell count (SCC), and mineral content were analyzed. Eight primiparous and 10 multiparous Murciano-Granadina goats free from IMI were included in the study. Health conditions of the participating animals were monitored for 16 d and then various unfavorable health situations that may arise on commercial farms were simulated to increase the chances of IMI. Once the IMI was confirmed, the experiment continued for another 16 d. Statistical analysis was conducted using a linear mixed model considering several periods regarding the establishment of the infection and whether it affected one or both glands in the animal. The establishment of IMI caused a significant increase of EC, SCC, and chlorides in the infected glands, whereas the sodium:potassium ratio and the ratio of EC between collateral glands showed significant increases only in bilaterally infected animals. The microorganisms that caused greater increases of EC were Staphylococcus aureus and a gram-negative bacterium. Changes due to other isolated microorganisms (coagulase-negative staphylococci and streptococci) were small. No significant differences in milk yield were determined. The significant effect of infection on EC in the affected glands suggests that the use of a system based on daily readings of EC could be useful in IMI detection of goats.

Analysis of the influence of variation factors on electrical conductivity of milk in Murciano-Granadina goats

The aim of this study was to obtain further knowledge on electrical conductivity (EC) of milk as a tool for detecting mastitis in goats. The effect of farm, parity, stage of lactation, and health status of the glands on EC, and the somatic cell count (SCC) of milk was analyzed. Additionally, relationships between EC and chemical composition and SCC were studied. Finally, characteristics of EC and SCC (sensitivity and specificity) as diagnostic tests used to detect mastitis were studied. One hundred and five Murciano-Granadina goats were enrolled in the study. Milk samples (by gland) were collected monthly for 7 mo on 3 farms in the southeastern Spain. To establish the health status, milk samples were aseptically collected before milking by gland. Foremilk (by gland) was collected to analyze EC, SCC, and chemical composition. Glands were classified according to the health status as free of mastitis, bacterial mastitis, or unspecific mastitis. The effects of farm, parity, and stage of lactation, as well as the interactions between health status and parity, parity and stage of lactation, and health status and stage of lactation were associated with EC. Changes in the milk's chemical composition (particularly of chloride ions) explained most of the variance in EC (R(2)=0.91). The strongest association between EC and SCC was found at SCC >2×10(6) cells/mL (r=0.42). The use of a single EC threshold for all animals and farms for detecting mastitis led to limited results for mastitis detection, which, in any case, favors negative predictive values over positive predictive values. This study revealed that factors, other than the health status, affecting EC hamper the use of an EC threshold for mastitis detection with sufficient specificity on all animals. Any detection system based on EC of milk should consider these factors, as well as specific variations for each of the animals.

The role of lactate dehydrogenase, alkaline phosphatase and aspartate aminotransferase in the diagnosis of subclinical intramammary infections in dairy sheep and goats

The objective was to investigate the changes occurring in the activities of the enzymes lactate dehydrogenase (LDH), alkaline phosphatase (ALP) and aspartate aminotransferase (AST) in sheep and goat milk as a result of subclinical intramammary infections (IMI) and to evaluate the use of these enzymes for the diagnosis of subclinical IMI in dairy sheep and goats. A total of 206 samples of sheep milk and 162 samples of goat milk, obtained from equal udder halves, were used in the study. For each species they were divided into two groups: a no-infection group and a subclinical infection group. Activities of LDH, ALP and AST were significantly higher in the subclinical infection group than in the no-infection group (P<0·05) in both sheep (LDH: 350·42±11·25 v. 120·91±4·41; ALP: 2773·43±105·18 v. 2189±94·24; AST: 29·57±0·74 v. 17·32±0·46) and goats (LDH: 354·07±13·33 v. 103·79±3·75; ALP: 311·13±25·74 v. 137·24±19·62; AST: 27·59±6·42 v. 15·87±0·45). The activity of LDH was identified as indicator for subclinical IMI in both sheep and goats. The optimum cut-off values for LDH activity, offering the highest diagnostic sensitivity (DSn) and diagnostic specificity (DSp), determined by receiver operating characteristic (ROC) analysis, were at 197 U/l, 185 U/l and 197 U/l for sheep, goats and both species, respectively. DSn for sheep, goats and both species at these cut-off values was 92·8%, 98·2% and 94·0%, whereas DSp was 95·4%, 96·3% and 96·3%, respectively. It was concluded that the determination of LDH activity in milk serum is a sensitive and reliable method for the detection of subclinical IMI in dairy sheep and goats.