Emotional stress caused by moving to unfamiliar surroundings inhibits oxytocin (OT) release and milk ejection in dairy cows, while blood concentrations of β-endorphin and cortisol are elevated (Bruckmaier et al. 1993). β-Endorphin and cortisol concentrations decrease with repeated relocation to unfamiliar surroundings while milking-related OT release and milk ejection gradually normalize (Bruckmaier et al. 1996). Exogenous cortisol has previously been shown to exert no inhibiting effect on milk ejection in cows (Mayer & Lefcourt, 1987). Therefore, it seems likely that the inhibition of milk ejection in cows – as in other species – is mediated by endogenous opioid peptides. The opioid antagonist naloxone abolishes the inhibiting effect of endogenous opioid peptides on OT release in several species (Haldar et al. 1982; Seckl & Lightman, 1987; Gilbert et al. 1992; Aurich et al. 1996).

Milk ejection is inhibited by α-adrenergic receptor stimulation in the mammary gland without reduction of OT release (Bruckmaier et al. 1997). Opioid-induced inhibition of OT release may be mediated by noradrenergic neurons via β-adrenergic receptors (Crowley & Armstrong, 1992). If adrenergic receptors are involved in the blockade of OT release in cows during milking in unfamiliar surroundings, the inhibition may be abolished by adrenergic blocking agents.

Cortisol synthesis is diminished by administration of metyrapone (Martindale, 1989). Because cortisol has a negative feedback effect on ACTH release, the release of ACTH and concomitantly of β-endorphin is elevated by metyrapone in the rat (Pettibone & Mueller, 1984). Thus, milk ejection should be indirectly inhibited by metyrapone administration via enhanced release of β-endorphin in the familiar barn.

Experiments were designed to investigate the importance of elevated concentrations of β-endorphin in unfamiliar surroundings for disturbed milk ejection in dairy cows.

Milk proteins have largely been considered as providing essential amino acids, but oligopeptides derived from milk proteins have been shown to possess biological functions. In vitro, opioid activity was first reported in bovine β-casein hydrolysate by Brantl et al. (1979). Precursors of biologically active peptides have been demonstrated in vivo after digestion of milk (Scanff et al. 1992). Peptides that inhibit platelet aggregation (Fiat et al. 1989), stimulate the immune system (Migliore-Samour et al. 1989), inhibit angiotensin I converting enzyme (Maruyama & Suzuki, 1982) and are involved in intestinal Ca solubilization and absorption (Sato et al. 1986) have also been isolated from bovine casein hydrolysates.

Bioactive peptides from whey proteins and their physiological effects have received less attention than those from casein. Peptides with opiate-like activity include the lactorphins, residues 50–53 in bovine and human α-lactalbumin and 102–105 in bovine β-lactoglobulin (β-lg) (Chiba & Yoshikawa, 1986; Yoshikawa et al. 1986; Antila et al. 1991). Yamauchi (1992) has reported that a peptide derived from β-lg induced contraction of guinea pig ileum longitudinal muscle in the absence of electric stimulation and agonist. The fragment, containing residues 146–149 of β-lg (His–Ile–Arg–Leu), was called β-lactotensin.

The purpose of this study was to determine whether β-lactotensin was released from bovine β-lg by in vitro proteolysis using different proteolytic enzymes. The pharmacological activity of this tetrapeptide was characterized in guinea pig ileum in vitro using a synthetic fragment.

Butyric acid fermentation in brine salted, semi-soft and hard cheeses (late blowing) can create considerable loss of product. Clostridium tyrobutyricum, a Gram-positive, sporeforming, anaerobic bacterium, has been identified as the causative agent (Klijn et al. 1995).

Lameness is a major welfare concern in dairy cattle. Estimates of the annual incidence of lameness range from 4 to 30%, and even in well managed herds as many as 15% of animals can be affected (Esselmont, 1990). In addition to the cost in animal suffering, lameness is accompanied by loss of production on a scale comparable, in temperate countries, with that caused by mastitis. Lost production, veterinary charges and milk discard costs coupled with reduced fertility or premature culling in turn make lameness a major economic factor in dairy farming. In the UK alone, the estimated cost in lost production is £44–£90 million per annum, equivalent to £10–20 per cow (Booth, 1989; Esselmont, 1990).

During lactogenesis in the goat, the onset of secretion of calcium into milk occurs at parturition (Thompson et al. 1995) at approximately the same time as the onset of secretion of parathyroid hormone-related protein (PTHrP) by the mammary gland (Ratcliffe et al. 1992); these events may be unrelated or PTHrP may be involved in calcium transport from blood to milk.

Parturition in goats is initiated by fetal secretion of cortisol (Flint et al. 1978) and maternal secretion of cortisol also increases (Paterson & Linzell, 1971). Injecting cortisol locally into the sinus of a mammary gland of the late-pregnant goat when the tight junctions between secretory epithelial cells appear to be ‘loose’, and injectate can reach the basolateral surfaces of secretory cells, stimulates an early tightening of these junctions (Thompson, 1996) as occurs naturally at parturition. This tightening can be produced by an increased concentration of ionized calcium in the extracellular fluid of the gland (Neville & Peaker, 1981).

The experiments reported here were undertaken to determine if cortisol injection stimulates the mammary gland to secrete both PTHrP and calcium before parturition.

Success in making a cheese acceptable in both flavour and texture depends partly on curd properties which determine the retention of fat and moisture and, thus, cheese yield and composition (Green & Grandison, 1993). When considering farmhouse and/or Appelation d'Origine Contrôlée cheese where milk treatments are not allowed, curd properties depend only on milk composition and clotting characteristics, which are subject to wide fluctuations over the year owing to the cow's stage of lactation and nutritional factors (O'Keeffe, 1984; Macheboeuf et al. 1993). These variations often result in seasonal differences in the chemical or sensory properties of the cheese (Kefford et al. 1995) which are sometimes difficult to understand (Grandison et al. 1985). Only a few studies have assessed the cheesemaking quality of milk by actually making ripened cheese; most studies report milk coagulation properties and curd firmness.

The object of this work was to study the influence of the chemical composition and clotting characteristics of the milk on the chemical and sensory properties of ripened cheeses when milk characteristics vary widely.

Plasmin (PLM; E.C. 3.4.4.14) is the major proteolytic enzyme normally present in bovine milk. From a technological point of view, PLM activity in milk is detrimental as it increases the proteolysis of casein to proteose peptones, and this results in reduced storage time, taste defects, loss of cheese yield and quality, and changes in the physicochemical properties of milk (for review, see Fox, 1992). Therefore a reduction of PLM activity in milk would be desirable. Plasminogen (PLG), the zymogen of plasmin, and PLM content are affected by several physiological and environmental factors, and by genetic factors such as breed (Richardson, 1983; Schaar, 1985; Politis et al. 1989; Benslimane et al. 1990). We have addressed the question of PLG polymorphism in dairy cattle.