Nissim Silanikove

HEAT STRESS IN LACTATING DAIRY COWS: A REVIEW

Our objective was to provide a review of factors influencing heat stress in lactating dairy cows and how it affects milk production. In warmer parts of the world, during summer months in the United States, and in other temperate regions, reduced milk production resulting from heat stress counteracts tremendous genetic progress achieved in increasing milk production. Genetic progress in milk production is closely related to increased feed intake. High feed intake results in raised metabolic heat increment. High metabolic heat increment requires effective thermoregulatory mechanisms to maintain body temperature in a thermoneutral zone and in physiological homeostasis. Cows can succumb to hyperthermia if they fail to maintain thermoneutrality. Accurate measurement of when cows enter heat stress is complicated because the responses to heat stress affect not only the energy balance, but also water, sodium, potassium and chlorine metabolism. Water, sodium, potassium and chlorine are important constituents of sweat, and sweating is a major, if not the most important, thermoregulatory mechanism used to dissipate excess body heat. Due to high metabolic heat increment, and especially in the warmer months, high-producing dairy cows may enter heat stress much earlier than their lower-producing counterparts and than currently thought, or extra heat has been accommodated by physiological adaptations. Should this be the case, then strategies to reduce heat stress must be developed to enable cows to express their full genetic potential. The thermoneutral zone, heat production and heat gain, heat dissipation mechanisms, and how the lactating cow responds to heat stress are discussed.

Effects of heat stress on the welfare of extensively managed domestic ruminants

Abstract High ambient temperatures, high direct and indirect solar radiation, and humidity are environmental stressing factors that impose strain on animals. This review concerns the heat stress–strain response of domestic ruminants from the viewpoint of animal welfare. Despite having well developed mechanisms of thermoregulation, ruminants do not maintain strict homeothermy under heat stress. There is unequivocal evidence that hyperthermia is deleterious to any form of productivity, regardless of breed, and stage of adaptation. The best recognized effect of raised body temperature is an adaptive depression of the metabolic rate associated with reduced appetite. Thus, in domestic ruminants a rise of body temperature marks the transition from aversive stage to noxious stage. Physiological (sweating, panting), hormonal (cortisol, thyroid gland activity), and behavioral thermoregulatory responses are discussed in respect to animal welfare. Factors such as water deprivation, nutritional imbalance and nutritional deficiency may exacerbate the impact of heat stress. The higher sensitivity of cattle to heat stress in comparison with sheep, and of animals at various productive stages in comparison with animals at maintenance is highlighted. Some practical measures that are applicable under extensive conditions, such as provision of shade shelter, are suggested.

The physiological basis of adaptation in goats to harsh environments

Abstract Goat living in harsh environments represents a climax in the capacity of domestic ruminants to adjust to such areas. This ability is multifactorial: low body mass, and low metabolic requirements of goats can be regarded as an important asset to them for it minimise their maintenance and water requirements, in areas where water sources are widely distributed and food sources are limited by their quantity and quality. An ability to reduce metabolism allows goats to survive even after prolonged periods of severe limited food availability. A skillful grazing behaviour and efficient digestive system enable goats to attain maximal food intake and maximal food utilisation in a given condition. There is a positive interaction between the better recycling rate of urea and a better digestion of such food in desert goats. The rumen plays an important role in the evolved adaptations by serving as a huge fermentation vat and water reservoir. The water stored in the rumen is utilised during dehydration, and the rumen serves as a container, which accommodates the ingested water upon rehydration. The rumen, the salivary glands and the kidney coordinately function in the regulation of water intake and water distribution following acute dehydration and rapid rehydration. Goats in the tropics, when possible, eat a diet composed of tree-leaves and shrubs (browse), which ensure a reliable and steady supply of food all year around, albeit, from a low to medium quality food. Some of the physiological features of ruminants defined as intermediate feeders like large salivary gland, the large absorptive area of their rumen epithelium, and the capacity to change rapidly the volume of the foregut in response to environmental changes are most likely responsible for the goat’s superior digestion capacity.

Effects of water scarcity and hot environment on appetite and digestion in ruminants: a review

Abstract The purpose of the present review is to provide an integrated examination of the effects of infrequent drinking, water restriction, and heat load on feed intake and utilization in ruminants. The above-mentioned limitations reduce appetite and increase feed utilization. Reduction in rumen motility, rumination activity and saliva secretion reduce passage rate, and hence increase the digestibility of structural carbohydrates. However, contrary to a commonly held view, these digestive responses are directly related to the imposed stress, rather than secondarily related to reduction in feed intake. Although water deprivation, water restriction and heat load similarly affect appetite and digestion, the physiological basis of each is different. Water restriction does not disturb plasma tonicity and its effect is mediated by modification of the food-related drinking. Water deprivation effects are mediated through elevation of plasma osmolarity and secondarily through increase in gut fill and ruminal Na concentration. Heat load effect is mediated through elevation of body temperature and secondarily through increase in gut fill. The response to heat stress is more diverse, since heat load affects both the energy and water metabolism, and varies due to differences among ruminants in insulation properties and body size. As water scarcity and high temperatures are characteristic of dry areas, interactions exist between these two factors, and some examples are given. Goats, having poor insulation capacity, and sheep, with excellent insulation capacity, represent two physiological models. Breeds of ruminants which are well adapted to arid environments demonstrate a greater capability than nondesert breeds to ameliorate the stressful effects induced by water deprivation and heat load. However, as a general rule, the negative effects of water deprivation and heat stress override the benefits from increased feed utilization.

Goats fed tannin-containing leaves do not exhibit toxic syndromes

Abstract The blood metabolic profile was examined in 2–3 year old non-lactating and non-pregnant Mamber goats consuming Quercus calliprinos (oak), Pistacia lentiscus (pistacia) and Ceratonia siliqua (carob) leaves to determine whether intake of tannin-rich fodder induces subclinical systemic toxicity. Total phenolic and condensed tannin content ranked in the order pistacia > oak > carob. Goats did not exhibit toxic effects following consumption of 10–23 g kg −1 day −1 of tannin-rich leaves. Metabolite blood concentrations did not differ from goats fed wheat straw, and were within the normal range. Certain serum metabolic indices that are known to be sensitive indicators of damage to the liver (gamma glutamyltranspeptidase, alkaline phosphatase, cholesterol) and kidneys (urea, uric acid, minerals) were within the normal range for goats. Thus, it appears that goats used in this study were well adapted to the nutritional environment and may consume large amounts of tannins (1.1–2.7 g per kg BW per day condensed tannins and 0.4–0.9 g kg −1 BW day −1 soluble phenolics) without suffering any ill effects.

Stress down regulates milk yield in cows by plasmin induced β-casein product that blocks K+ channels on the apical membranes

Stress and stress related hormones such as glucocorticoids inhibit lactation in cows. In the present study we propose a novel mechanism connecting stress with plasminogen-plasmin system (PPS) (an enzymatic mechanism in milk, which leads to the breakdown of the major milk protein casein). We show that stress activates the PPS leading to an increase in plasmin activity, and that a distinct plasmin-induced beta-casein breakdown product (fraction 1-28) is a potent blocker of potassium channels in mammary epithelia apical membranes. The reduction in milk production due to dehydration stress or glucocorticoid (dexamethsone) was correlated with the activities of plasmin and channel blocking activity in the milk of the tested cows. The notion that the axis Stress-PPS-beta-casein fraction 1-28 is responsible for the reduction in milk yield is supported by the results of experiments showing that injecting solution composed of casein digest enriched with beta-casein fraction 1-28 to the udder lumen leads to a transient reduction in milk production. Furthermore, injecting a pure beta-casein fraction 1-28 to the udder lumen of goats lead also to a transient reduction in milk production with kinetics that was similar to the kinetics observed in cows.

Interactions among tannins, supplementation and polyethylene glycol in goats given oak leaves: effects on digestion and food intake

Effects were studied on food intake and diet apparent digestibility of giving to goats once daily a basal diet rich in tannin from inclusion of leaves of Quercus calliprinos either supplemented with a high carbohydrate or a high protein food. Also interactions with polyethylene glycol (PEG) were investigated. The results of the present work confirmed our presumption that the content of tannin in some Mediterranean browse is so high that it may negatively affect the utilization of protein in supplementary foods. Neutralizing the tannins with once-daily provision of PEG proved to be an effective means of preventing the negative effect. Providing 10 g/day PEG to goats given Quercus calliprinos leaves ad libitum and supplemented with 300 g/day concentrates containing 160 g crude protein per kg DM increased digestible crude protein intake by 50 g/day. When the concentrate food was given to goats, leaf dry-matter intake decreased significantly (from 664 to 565 g/day) and the goats lost weight rapidly. Therefore, supplementing tannin-rich leaves with concentrate food is recommended only if done in combination with PEG. High protein supplementation increased leaf (from 664 to 844 g/day) and digestible protein intakes (from 4·8 to 92·3 g/day) but a considerable portion of the protein supplementation was wasted due to interaction with tannins. PEG may allow economies in the use of such high-cost foods due to the greater efficiency of protein utilization (digestible crude protein intake increased from 92·3 to 122 g/day) of the supplementary food and to increased intake and protein utilization of the basal leaf diet (from 844 to 1023 g/day).

Utilization of low quality resources by small ruminants in Mediterranean agro-pastoral systems: the case of browse and aftermath cereal stubble

Abstract Browse and cereal stubble represent the two most important resources for grazing small ruminants in dry Mediterranean areas. The purpose of the present review is to provide updated information regarding their nutritional value. In a mixed Mediterranean environment, browse represents at least 40% of goats diet. Most browse species in the Mediterranean are rich in tanniferous phenolic substances. Polyethylene glycol (PEG) can bind tannins irreversibly over a wide range of pH and is efficient in alleviating the negative effects of tannins. Supplementing with PEG improves intake and digestibility in grazing goats and sheep and has the potential to be economically profitable. The chemical composition of wheat stubble is affected by the cultivar of wheat and climate, but not tillage management. The quality of stubble from early maturing is lower than from late maturing cultivars. Stubble contains more protein in years of lower rainfall. If grains escaped from the harvest combine (2% of grain yield) are included, digestibility of OM from different components ranges between ±80% (grain) to ±40% (stem). Also, the energy requirement of sheep grazing on stubble may be 70% higher than in shaded feedlot. Therefore, the body condition changes of sheep grazing on stubble exhibit a cyclic pattern consequent with temporal changes in nutritive quality. Because stubble grazing is concurrent with the onset of oestrous season, supplementation with grains from legume species-rich in degradable protein-is needed to prevent impairment of body condition. Supplementing browsing goats with PEG, and sheep grazing cereal stubble with moderate amounts of legume grain, may enable the use of these traditional resources in the frame of sustainable production systems.

Short-term changes in eating patterns explain the effects of condensed tannins on feed intake in heifers☆

Ingestion of condensed tannins decreases feed intake in ruminants. Polyethylene glycol (PEG) forms high-affinity complexes with tannins. In two experiments carried out on Holstein heifers, quebracho (Q) from the Aspidosperma quebracho served as source of condensed tannins. The aims of the study were (i) to quantify the effect of Q on feed intake and eating behaviour in cattle fed complete mixed diets (CMDs); (ii) to clarify if changes induced in ingestive behaviour and feed intake by Q in cattle can be reversed by feeding PEG; and (iii) to clarify if the decrease in feed intake is associated with short-term (astringency, post-ingestive malaise) or longer-term effects. In experiment 1, 500 g/day of Q was found to be the minimal dose that decreased feed intake in heifers. A ratio of PEG:Q equal to 1:12.5 did not fully restore feed intake. In experiment 2, four heifers received a random sequence of four rations in a Latin-square design with feeding cycles of ca. 7 days: CMD containing no supplements (C), or supplemented with 625 g/day of Q without PEG (Q), with 625 g/day of Q and 250 g/day of PEG (Q-PEG), or with 250 g/day of PEG without Q (PEG). Individual rations were continuously weighed in the trough and the behaviour of heifers was observed for 180 min after distribution of CMD. Overall, feeding Q was associated with lowered feed intake and shorter duration of eating bouts, mainly of the first eating bout, immediately after distribution of the diet. A larger portion of the diet was consumed subsequent to 180 min after distribution in Q-fed heifers. Eating rate and the water to food ratio were not affected by Q. The effects of Q on feed intake were attenuated by feeding PEG. Heifers adapted effectively to condensed tannins by increasing the number of eating bouts and the portion of diet consumed subsequent to 180 min after distribution, so that no differences in feed intake were noted on the last day of each feeding cycle. Data are interpreted to show that: (i) negative effects of Q on feed intake derive from astringency of CT and short-term post-ingestive malaise; (ii) the increased number of eating bouts and their wider partition throughout the day are means to preserve the ruminal environment in Q-fed heifers; (iii) PEG has the potential to neutralize negative effects of condensed tannins in cattle.

Acute heat stress brings down milk secretion in dairy cows by up-regulating the activity of the milk-borne negative feedback regulatory system

BackgroundThe objective of this study was to determine if acute heat stress (HS) decreases milk secretion by activating the milk-borne negative feedback system, as an emergency physiological response to prevent a life-threatening situation. To induce HS, summer acclimatized dairy cows were exposed to full sun under mid-summer Mediterranean conditions, with and without conventional cooling procedures.ResultsExposure to HS induced a rapid and acute (within 24 h) reduction in milk yield in proportion to the heat load. This decrease was moderated by cooler night-time ambient temperature. The reduction in milk yield was associated with corresponding responses in plasminogen activator/plasminogen-plasmin activities, and with increased activity (concentration) of the (1–28) N-terminal fragment peptide that is released by plasmin from β-casein (β-CN (1–28)). These metabolites constitute the regulatory negative feedback system. Previously, it has been shown that β-CN (1–28) down-regulated milk secretion by blocking potassium channels on the apical aspects of the mammary epithelial cells.ConclusionHere we demonstrate that the potassium channels in mammary tissue became more susceptible to β-CN (1–28) activity under HS. Thus, the present study highlighted two previously unreported features of this regulatory system: (i) that it modulates rapidly in response to stressor impact variations; and (ii) that the regulations of the mammary epithelial potassium channel sensitivity to the inhibitory effect of β-CN (1–28) is part of the regulatory system.