Influence of tissue origins and external microenvironment on porcine foetal fibroblast growth, proliferative life span and genome stability.

One of the challenges of manipulating genes in primary cells is that the cells have a finite proliferation capacity. This, combined with the lower gene targeting efficiency of somatic cells, makes identification of targeted clones very difficult. The objective of this study was to establish a system that allows porcine foetal fibroblasts to reach their maximal proliferation capacity in vitro. The influence of fibroblast origin, stage of foetal development, cell seeding densities and concentration of foetal bovine serum (FBS) on the population doublings, the percentage of beta-galactosidase-activity-positive cells and the genome stability of foetal fibroblasts during in vitro culture was investigated. It was found that porcine foetal fibroblasts could be cultured for over 80 population doublings in the appropriate culture system. Fibroblasts from earlier stages of foetal development were better candidate cells than those from the later stages. Cells from the heart were more actively proliferative and more resistant to replicative senescence than those from the liver. Compared to 10% FBS content, 15% FBS provided better homeostatic support, not only to proliferative performance, but also in maintaining a normal karyotype. In addition, the proliferative life span of porcine foetal fibroblasts is also dependent on seeding density of the culture.

Determination of true digestive utilization of phosphorus and the endogenous phosphorus outputs associated with soybean meal for growing pigs.

The objectives of this study were to determine true P digestibility, the gastrointestinal endogenous P outputs associated with soybean meal (SBM), and the role of the large intestine in P digestion in growing pigs. Four Yorkshire barrows, with average initial and final BW of 40 and 58 kg, were fitted with a simple T-cannula at the distal ileum and fed four diets according to a 4 x 4 Latin square design. The diets were cornstarch-based and contained four levels of P (0.098, 0.196, 0.293, and 0.391% on a DM basis) from solvent-extracted conventional SBM. Chromic oxide (3.5 g/kg of diet, as-fed basis) was included as a digestibility marker. Each experimental period consisted of 8 d with a 4-d adaptation period and a 4-d collection of representative ileal digesta (2 d) and fecal (2 d) samples. True ileal and fecal P digestibility values and the ileal and fecal endogenous P outputs associated with SBM were determined by the regression analysis technique. There were no differences (P > 0.05) in true P digestibility values (ileal, 59.0 +/- 8.3 vs. fecal, 51.3 +/- 7.9%, n = 16) and endogenous P outputs (ileal, 0.59 +/- 0.18 vs. fecal, 0.45 +/- 0.21 g/kg of DMI, n = 16) between the ileal and the fecal levels. The endogenous fecal P loss accounted for 8.1 and 17.6% of the NRC (1998) recommended total and available P requirements in growing pigs, respectively. In conclusion, approximately 51% of the total P in conventional SBM is digested in growing pigs. The large intestine does not play an important role in the digestion of P associated with SBM in the growing pig. The fecal loss of the gastrointestinal endogenous P is an important route of P excretion in the growing pig.

Novel methodology allows simultaneous measurement of true phosphorus digestibility and the gastrointestinal endogenous phosphorus outputs in studies with pigs.

Methodology was developed for measuring the gastrointestinal endogenous phosphorus (P) outputs and true P digestibility values in studies with piglets. Four barrows, average initial body weight 6.8 kg, were fitted with a simple T-cannula at the distal ileum and fed four diets according to a 4 x 4 Latin square design. Four cornstarch-based diets containing four levels of P (1.1, 2.1, 3.2 and 4.3 g/kg diet) on a dry matter (DM) basis were formulated from soybean meal (SBM). Each experimental period comprised 8 d with a 4-d adaptation and 4-d collection of ileal digesta and feces. The apparent ileal and fecal P digestibility values in SBM were affected (P < 0.05) by P levels in the assay diets. The ileal and fecal P digestibility values increased from -24.8 to 37.1% and from 18.8 to 42.5%, respectively, as P contents increased from 1.1 to 4.3 g/kg DM diet. Linear relationships (P < 0.05), expressed as g/kg DM diet intake, between ileal and fecal outputs and dietary inputs of P, suggested that the endogenous P outputs can be determined by linear regression analysis. The endogenous P output was higher (P < 0.05) in ileal digesta than in feces (0.86 +/- 0.09 vs. 0.31 +/- 0.06 g/kg DM diet intake). There was no difference (P > 0.05) between the true ileal (50.7 +/- 7.1%) and fecal (48.5 +/- 5.4%) P digestibility values in SBM. These results suggest that differences in P contents between assay diets are primarily responsible for the large variability in apparent P digestibility values reported within the same ingredient. Apparent digestibility values underestimate the true digestive utilization of P by approximately 25%. True rather than apparent P digestibility values should be determined and used in diet formulation for pigs. In addition, this study shows that the gastrointestinal endogenous P output is important in whole-body P requirement and homeostasis.

Pigs expressing salivary phytase produce low-phosphorus manure.

To address the problem of manure-based environmental pollution in the pork industry, we have developed the phytase transgenic pig. The saliva of these pigs contains the enzyme phytase, which allows the pigs to digest the phosphorus in phytate, the most abundant source of phosphorus in the pig diet. Without this enzyme, phytate phosphorus passes undigested into manure to become the single most important manure pollutant of pork production. We show here that salivary phytase provides essentially complete digestion of dietary phytate phosphorus, relieves the requirement for inorganic phosphate supplements, and reduces fecal phosphorus output by up to 75%. These pigs offer a unique biological approach to the management of phosphorus nutrition and environmental pollution in the pork industry.

Circadian variation of portal, arterial and venous blood levels of melatonin in pigs and its relationship to food intake and sleep.

Circadian levels of melatonin were determined in the hepatic portal vein, cranial vena cava, and the lower aorta of ten juvenile pigs. Blood was sampled every hour for a total of 24 hr via temporary cannulas introduced into blood vessels under anesthesia. No peak levels of melatonin were found in the mid-scotophase, but hepatic portal concentrations peaked at 06.00 hr. Overall levels of melatonin were highest in the hepatic portal vein (range 35-65 pg/mL), followed by an artery (range 30-55 pg/mL) and the vena cava (range 25-35 pg/mL). Levels of melatonin exhibit strong variation between individual pigs, but generally the average levels from all three sources follow each other's time course. However, on occasion, melatonin levels in the hepatic portal vein varied independently from the levels in the vena cava. Large portal peaks were usually preceded by a feeding period and were associated with a subsequent period of sleep. The data indicate that: 1) there is no clear circadian rhythm of melatonin in the peripheral blood of pigs, 2) relatively little melatonin is metabolized during the first liver passage, 3) food intake may elevate melatonin levels in the hepatic portal vein, and 4) increased levels of melatonin originated in the gastrointestinal tract may induce sleep.

Melatonin concentrations in the luminal fluid, mucosa, and muscularis of the bovine and porcine gastrointestinal tract.

Melatonin concentrations were measured in serum, luminal fluid, and tissues of the mucosa and muscularis of the entire bovine and porcine gastrointestinal tract (GIT). In both species, GIT levels profoundly exceeded serum levels. In pigs, melatonin was lowest in the luminal fluid and highest in the mucosa. No difference was found in various layers of bovine GIT. Compared to pigs, cows had higher melatonin levels in the stomach and ileum, but lower in the cecum and colon. There was no difference in melatonin levels between anterior and posterior segments of bovine GIT, whereas pigs exhibited several fold higher concentration of melatonin in the posterior segment (cecum and colon). Conversely, melatonin values in the anterior segment were significantly higher in cows, but in the posterior segments porcine values were higher. In cows, concentrations in the mucosa correlated with levels in the muscularis. Melatonin levels in the mucosa and muscularis were higher in the rumen and reticulum than in the omasum and abomasum. The species-specific levels and a distinct distribution of melatonin in the layers of the digestive tube indicates that this indole may be involved in the modulation of gastrointestinal function of monogastric as well as polygastric ungulates, albeit in a different capacity.

Relationships between serum IGF-I concentrations and piglet development or neonatal viability following porcine somatotropin (pST) and insulin administration to gestating gilts.

This study was designed to evaluate the effects of exogenous treatment with pST, insulin and their combination on periparturient serum IGF-I levels, prenatal piglet development and viability. Pregnant Yorkshire gilts were injected daily with either 5 ml of saline (C), n = 23; 5 mg pST (P), n = 23; 0.50 IU/kg of insulin (I), n = 23; or pST plus insulin at the above dosage, according to 2 x 2 factorial design from Day 30 to 70 of gestation. All gilts were sacrificed on Day 113 of gestation. Peripartum IGF-I serum levels were determined by RIA following a 36 h incubation in 0.2 M gly-gly HCL. Recovery of human rIGF-I standard was > 95%, while the intra-assay CV was 5.74%. Measures of piglet viability were compared using Randall's adaptation of Apgar score for human neonates. Piglet weight and crown-to-rump length were determined prior to dissection. Treatments (P, I and P + I) elicited highly significant increases in maternal serum IGF-I concentrations (321.9, 337.0, 375.0 vs 247.6 ng/ml; P = 0.0001) on Day 113 of gestation. Nonsignificant differences were detected in piglet serum IGF-I (94.8, 102.6, 110.2 vs 92.2 ng/ml; P = 0.06). These results revealed no relationship between piglet weight and maternal (r = 0.03) or piglet serum IGF-I levels (r = 0.08). Only a weak association between gilt and piglet serum IGF-I concentrations (r = 0.26) was detected. Injections with pST and or insulin did not influence piglet viability scores (P = 0.74). Viability scores were highly correlated with piglet weight (r = 0.66), crown -rump length (r = 0.70), but not with IGF-I concentrations in gilt (r = 0.09) and piglet serum (r = 0.16). Body weights, crown -rump length and visceral organ weights of piglets did not differ between control and hormone -treated gilts (P >/= 0.05). These results indicate 1) that there was no direct treatment effects on in utero piglet development or neonatal viability; 2) that IGF-I production in gilt and piglet compartment is independent, suggesting fetal endocrine autonomy regarding IGF-I production; and 3) that the usual low IGF-I concentrations in mid-late gestation in swine could be replenished by maternal pST and or insulin therapy.

Melatonin concentrations in serum and tissues of porcine gastrointestinal tract and their relationship to the intake and passage of food.

Melatonin concentrations were determined in serum and 10 segments of the gastrointestinal tract (GIT) of 48 pigs (100 kg weight). The animals were fasted for 30 hr and then sacrificed 0, 1, 2, 5, 10, and 20 hr after refeeding. Peak amount of gastric digesta (2,428 g) and ileum digesta (850 g) were observed 1 hr and 5 hr, after refeeding, respectively. Conversely, colon content reached a minimal weight (726 g) at 2 hr after refeeding. Serum levels of melatonin increased from 3.4 pg/ml to 15.5 pg/ml (peak 5 hr after refeeding). Melatonin levels in GIT tissues before refeeding varied from 23.8 pg/g (stomach-fundus) to 62.1 pg/g (rectum). Increasingly higher levels of melatonin were detected in the distal segments of the GIT. Higher melatonin levels after refeeding were observed in most GIT tissues except the rectum. In most tissues, peak melatonin values were detected 5 hr after refeeding. A significant change in weight of digesta across time (P < 0.05) was detected in the stomach, ileum, and cecum. Similar changes in melatonin levels across time were found in most tissues except the esophagus, stomach (cardia and pylorus), and rectum. Adjacent GIT tissues exhibited similar (P < 0.05) melatonin levels. The GIT melatonin levels correlated best with the variation of digesta weight in the ileum. In addition, the increase of serum melatonin levels correlated best with the increase of GIT melatonin levels in the distal part of the GIT. Our results suggest that melatonin produced in the ileum, cecum, and colon may contribute significantly to the short-term increase of serum melatonin levels observed after refeeding.

Effects of dietary protein percentage and beta-agonist administered to prepubertal ewes on mammary gland growth and hormone secretions.

The effects of dietary protein and beta-agonist, (L-644,969) on mammary growth from weaning to puberty, hormone secretions, and milk yield were studied. Twelve lambs were assigned to each treatment in a 2 x 2 factorial arrangement with dietary protein at 15 or 20% and beta-agonist at 0 or 1 ppm of concentrate. Lambs were fed pelleted concentrate to achieve a target weight gain of 260 g/d. The treatment period continued for 102 d, with protein starting on d 1 and beta-agonist on d 20. Five lambs in each group were slaughtered at the end of treatment to investigate mammary growth before puberty. The remainder were maintained, and, after lambing, daily milk yield was recorded for 7 wk and ewes were then slaughtered. In prepubertal lambs, compared with control, the 20% protein diet had no effect on any variable measured in the mammary glands, whereas beta-agonist increased (P < .05) RNA:DNA ratio. In lactating ewes, the 20% protein diet enhanced mammary gland weight, parenchyma, parenchymal dry fat-free tissue (P < .05), and parenchymal fat (P < .01). The beta-agonist reduced mammary gland weight (P < .01), parenchyma, parenchymal dry fat-free tissue (P < .05), and parenchymal fat (P < .01). There was a nonsignificant trend for increased milk yield for ewes fed the 20% protein diet and decreased milk yield for beta-agonist. The beta-agonist increased somatotropin concentration, but there was no evidence that increased somatotropin concentration induced mammogenesis in lambs. In conclusion, increased dietary protein may play a role in stimulating mammogenesis in rapidly growing lambs before puberty.

The effect of caffeine on mammary gland development and milk yield in primiparous sows.

Pregnant Yorkshire gilts (n = 42) were fed caffeine (6 g/d) or served as controls from d 60 of pregnancy until d 4 postpartum to test the effect of caffeine on mammary gland development, milk yield, and feed consumption. Caffeine reduced voluntary feed intake (P = .001) and body weight gain (P = .001) of gilts from d 60 to 109 of gestation. Pig birth weight in the treated group was less than (P = .01) that in the control group. However, pig viability score at birth was not affected by maternal caffeine ingestion. For assessing mammary gland DNA, RNA, dry fat-free tissue (DFFT), fat, and protein content, four sows from the caffeine group and three controls were slaughtered on the 1st d of lactation. Immediately after slaughter, mammary systems were removed, separated by gland, and dissected free of skin, muscle, and fatty pad, which had not been invaded by glandular tissue. The DNA and RNA content were evaluated in DFFT. Caffeine increased mammary RNA content (P = .023) and milk yield (P = .001) on d 1 of lactation. However, DNA, DFFT, fat, and protein were not significantly increased, although values were somewhat greater in the treatment group (approximately 82%). On d 21 of lactation, milk yield of treated sows did not differ from that of controls. The increased milk yield on d 1 of lactation was due to increased mammary epithelial cell activity and cell numbers. These results indicate that caffeine feeding can have a positive effect on porcine mammary gland development as well as milk yield.

Influence of penning type and feeding level on sexual behavior and feet and leg soundness in boars.

Ninety-six Yorkshire males at 28 d of age were placed on a pre-test feeding regimen (22% CP) of either ad libitum (A) access to feed or a restricted (R, 85% of A) diet. All pigs were housed in groups of four until approximately 30 kg body weight. The boars were then placed under test and assigned to a group pen (GP) containing eight boards or to individual pens (IP) and fed a 16% CP diet at A or R levels. Feeding types during pre-test and test phases were, therefore, ad libitum followed by ad libitum (AA), ad libitum: restricted (AR), restricted: ad libitum (RA), and restricted: restricted (RR) for each of the two (IP and GP) housing types. All boars were weighed every 2 wk to determine the feeding level and ADG. The pen floors were partly slatted with water nipples in the slatted areas. Areas available for each board were 1.63 and 2.15 m2 in IP and GP, respectively. Sexual behavior, semen characteristics, and feet and leg scores were recorded between 150 and 240 d of age. The IP boards required longer (P < .05) contact with receptive gilts before mating, made more (P < .01) ano-genital sniffings, and attempted more (P < .10) incorrect mounts than GP boars. The GP boards had a higher (P < .01) mating score, younger (P < .001) age at completion of the mating test, and lower (P < .01) total sperm count and sperm concentration (P < .001) than IP boars. The AA boards exhibited less (P < .10) chomping and salivation than boars on other feeding regimens.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of light dark cycles on estradiol-17 beta induced luteinizing hormone patterns of the prepuberal gilt.

Two groups of Yorkshire gilts (110 d of age) were maintained in two light regimens. Both light regimens consisted of 14 h of light and 10 h of darkness, but were 180 degrees out of phase. Gilts in Group 1 received light from 1200 to 0200 and gilts in Group 2 from 2400 to 1400. At approximately 140 d of age each group was divided into four subgroups of eight gilts each (1A, 1B, 1C, 1D or 2A, 2B, 2C, 2D). All gilts were blood sampled at 2-h intervals for 5 d commencing on d 142. The four subgroups received a single injection of estradiol (15 micrograms/kg body weight) on d 143 at either 2400 (A), 0600 (B), 1200 (C), or 1800 (D). For pigs in Groups 1A and 1D, the injection of estradiol coincided with the animals' "subjective day" and the injections given to Groups 1B and 1C with their "subjective night." When estradiol-17 beta (E2) was administered to the gilts during their subjective day the LH profile showed one peak, whereas when E2 was administered during dark hours the profile exhibited two peaks (P < .0001). In Group 2 for which the light cycle was reversed, the well-defined spikes of LH were found to coincide with the injections of estradiol administered during the dark hours. Smaller biphasic peaks of LH occurred when injections of estradiol coincided with the light hours.(ABSTRACT TRUNCATED AT 250 WORDS)

Factors affecting excretory behavior of pigs.

A 2(4) factorial experiment with six pens per treatment was conducted to examine the factors affecting the excretory behavior of growing-finishing pigs. The factors investigated were partition type (open or closed), pig density (9 or 14 pigs/pen, size: 2 m x 4.5 m), position of nipple drinker in the pen (back wall of the pen or side in front of slatted area), and prior experience of pigs (training or no training). A total of 1,104 pigs at a weight interval of 28.4 +/- .2 to 91.4 +/- .4 kg were used in this study. Pen cleanliness was assessed by a dung scoring system, and growth rate was determined over the growing-finishing period. Partition type, nipple drinker position, or prior training of pigs had no effect on growth rate. Stocking pigs at 14 pigs/pen reduced growth rate (P < .05) compared with 9 pigs/pen (.80 vs .83 kg/d). Significant differences for pen dirtiness were found for partition type. Pens with closed partitions were cleaner than those with open partitions (P = .0001) and pens became significantly dirtier as pigs grew older or heavier (P < .01). There was a significant interaction effect between pen partition and pig density as well as an interaction among pen partition, pig density, and water position (P < .05).

Effects of diaoxinxuekang on ascites in broilers.

To investigate whether Diaoxinxuekang (a Chinese medicine that is reported to improve blood circulation) plays a role in preventing ascites in broilers, day-old male broilers were divided randomly into four groups, each with seven replicates, and reared for 40 days. The birds were housed in a brooder room from Day 1 to 21 and then reared in an environmental chamber room under low temperatures. Diaoxinxuekang was added to rations at the rate of 0, 500, 1,500, and 3,500 mg/kg as Treatments 1 to 4. When Diaoxinxuekang was added to rations, body weight in the first 3 wk was increased significantly, but feed consumption remained unchanged. Heart weight was not significantly different between control and treatments, but liver weight in the control and 500 mg/kg group was heavier than in Treatments 3 and 4. Within treatment, heart weight of the normal broiler was less than that of the broiler with ascites. Treatment 4 showed significantly (P < .05) less ascites than Treatments 1, 2, and 3 in the processing examination. The results present evidence that 3,500 mg/kg Diaoxinxuekang reduces the incidence of ascites in broilers.

Evaluation of long-term somatotropin implants in finishing pigs.

Ninety pigs were used to investigate the efficacy of long-term implants of porcine somatotropin (pST) in improving growth, feed:gain ratio, and carcass characteristics in pigs at three dose levels (0-, 100-, and 200-mg pST implant) from 71 to 99 kg live weight. The use of long-term implants did not alter (P > .05) growth rate. Administration of the 200-mg pST implant resulted in a 15% reduction in feed consumption, and this reduction was significant (P < .05). The feed:gain ratio was improved (P < .05) in pigs that received the 200- compared with 0-mg pST implant (3.2 vs 2.62 of kg feed/kg of gain). In pigs that received the 200- or 100-mg pST implant, there was a reduction (P < .05) in carcass weight; however, carcass length was similar (P > .05) regardless of pST treatment. Administration of the 200-mg pST implant resulted in 25 and 38% reductions (P < .05) in last rib fat and leaf fat compared with the 0-mg pST implant. The weights of kidneys and head were increased by the pST administration. The weights of wholesale cuts were not affected by the administration of the pST implant. However, separable skin and fat from the ham, loin, and picnic were lower (P < .05) in pigs that received the 200-mg pST than in pigs that received the 0-mg pST implant. Meat color and structure were similar across pST treatments, indicating that the use of long-term pST implants was not detrimental to meat quality.(ABSTRACT TRUNCATED AT 250 WORDS)

Variables related to the progress of parturition and probability of stillbirth in swine.

Sow and piglet variables related to probability of stillbirth and to viability score were analyzed in litters from 98 multiparous Yorkshire sows. Immediately after the birth of each piglet, viability was scored using Randall's method. Sow variables related to the probability of stillbirth were average birth weight of the litter (p = 0.0001), sow age (p = 0.001), sow condition score (p = 0.003), length of gestation (p = 0.005), and number of piglets in the litter (p = 0.01). Sow variables related to average viability score were average birth weight of the litter (p = 0.001), standard deviation in birth weight in the litter (p = 0.02), sow age (p = 0.03), sow condition score (p = 0.03), and length of gestation (p = 0.03). Piglet variables related to probability of stillbirth were piglet hemoglobin (p = 0.0001), position in the birth order (p = 0.0001), broken umbilical cord (p = 0.0004), and preceding birth interval (p = 0.0004). Piglet variables related to viability score were piglet hemoglobin (p = 0.0001), position in the birth order (p = 0.0001), broken umbilical cord (p = 0.0001), preceding birth interval (p = 0.0001), and birth weight (p = 0.004). Preceding birth interval was related to whether the piglet was live or stillborn (p = 0.0001), to position in the birth order (p = 0.003), and to the sex of the piglet (p = 0.03).The results demonstrated that sow and piglet variables were highly correlated to probability of stillbirth and to viability score. In addition it was also found that the probability of stillbirth was not associated with the duration of farrowing but with the number of piglets in the litter and piglet hemoglobin level. This study also found that lower weight piglets tend to have poor viability, but are not more prone to stillbirth as commonly suggested. These low viability piglets may survive if the necessary care is given during the farrowing process.

Effect of oxygen and neostigmine on stillbirth and pig viability.

In this experiment, 98 multiparous Yorkshire sows blocked on farrowing date were randomly assigned to four treatments in a 2 x 2 factorial arrangement. Oxygen inhalation (6 L/min) by the sow was tested in an effort to reduce stillbirth rate and improve pig viability. This study also tested the effect of increasing uterine contractions using neostigmine (5 mg) to determine whether simultaneous administration of oxygen to the sow could improve the inconsistent response of stillbirth rate to neostigmine. Pig viability was assessed using viability scoring and blood gas analysis of samples obtained from the suborbital sinus immediately after birth. The farrowings averaged 12.2 pigs/litter, 7.8% stillbirths, and 3.5% low viability (viability score < or = 6) pigs. Treatment had no effect on stillbirth rate or pig viability. Oxygen treatment increased pO2 (P = .0002), increased pCO2 (P = .02), and decreased pH (P = .02) in sow venous blood sampled after the birth of the last pig, but it had no effect on pig venous blood gases. Neostigmine treatment had no effect on either sow or pig venous blood gases. Oxygen treatment doubled the length of the first birth interval after the start of treatment (P = .003) but had no effect on remaining birth intervals. Neostigmine had no effect on birth interval. It is suggested that the effect of oxygen on birth interval is the reason for the lack of improvement in stillbirth rate.

Effect of chronobiological alteration of the circadian rhythm of prolactin and somatotropin release in the dairy cow.

The objective of this study was to determine if a skeletal photoperiod administered at the appropriate time of a 24-h day could stimulate prolactin and somatotropin release in dairy cattle. Cows in mo 8 of gestation were exposed to either 12 to 13 h of continuous light or to three skeletal photoperiods consisting of a total of 8 h of light. Cows in the skeletal photoperiod light regimens received 6 h of light from 0500 to 1100 h and a 2-h light pulse at either 1500 to 1700 h, 1800 to 2000 h, or 2100 to 2300 h. Cows exposed to the light regimen pulse at 1800 to 2000 h exhibited a circadian rhythm of prolactin and somatotropin release. The mean prolactin and somatotropin concentrations were also higher in this treatment. It is concluded that a circadian rhythm with a photosensitive phase is present for prolactin and somatotropin release in the lactating dairy cow. The photosensitive phase for both hormones occurs between 13 and 15 h after subjective dawn. The expression of the circadian rhythm of these hormones depends on the photoperiod to which cows are exposed.

Effect of chronobiological manipulation of lactation in the dairy cow.

The objective of this study was to determine if chronobiological manipulation of the environment through the use of skeletal photoperiods could enhance milk production of the dairy cow. Cows in their 8th mo of gestation were maintained in either a control light regimen (12 to 13 h continuous light) or three skeletal photoperiods exposed to a total of 8 h of light. Cows in the skeletal photoperiods received 6 h of light from 0500 to 1100 h and a 2 h light pulse between 1500 and 1700 h (pulse 1500 to 1700 h), 1800 and 2000 h (pulse 1800 to 2000 h), or 2100 and 2300 h (pulse 2100 to 2300 h). Cows were milked twice daily and milk weights recorded. Weekly milk samples were analyzed for fat, protein, lactose, and SCC. Milk progesterone was monitored for the first 60 d after calving to determine return to estrus. Total electrical consumption for lighting the different light regimens were monitored throughout the lactation. Cows in the light regimen of pulse 1800 to 2000 h exhibited a higher persistency of lactation and a higher feed efficiency than the cows in the other light regimens. There were no differences between treatments in milk fat, protein, lactose, or SCC. The total electricity used to light pulse 1800 to 2000 h was 50% less than that used to light the control light regimen. It is concluded that light is essential between 13 to 15 h after subjective dawn for increasing persistency of lactation. Further, milk production of the dairy cow can be profitably enhanced through the use of chronobiological principles.

Sow wastage: reasons for and effect on productivity.

The purpose of this study was to examine the reasons for, the rate and the effect of sow culling on productivity. Sow removal or wastage was investigated by means of producer questionnaires and by detailed production data recorded on 30 swine farms for two years. The sow removal rate was high (mean = 44.2%) with a wide herd-to-herd variation (range = 16% to 100%), and correlated negatively with litter size. Reproductive failure was the most common cause of culling cited by producers. It was concluded that sows on many Ontario farms were being culled prior to reaching their reproductive potential.