Udder health of dairy cows fed different dietary energy levels after a short or no dry period without use of dry cow antibiotics.

Reports on the effects of length of dry period (DP) on udder health of cows that were not treated with dry cow antibiotics are scarce. Additionally, the effects of a reduced dietary energy level for cows with a 0-d DP on udder health have not yet been studied. The aims of this study were (1) to compare effects of a 0-d or 30-d DP without use of dry cow antibiotics on udder health across the DP and subsequent lactation in dairy cows fed different dietary energy levels and (2) to evaluate associations between udder health and metabolic status of dairy cows. Five weeks before the expected calving date, Holstein-Friesian dairy cows (n = 115) were blocked for parity, expected calving date, and milk yield and somatic cell count (SCC) at their 2 last test days and were randomly assigned to 2 DP lengths: 0-d DP (n = 77) or 30-d DP (n = 38). Quarter milk samples were taken in wk 5 prepartum and in wk 1 and 5 postpartum. Proportion of quarters with elevated SCC (SCC ≥200,000 cells/mL) and proportion of udder pathogens in quarter milk samples did not differ between DP lengths among weeks. After calving, 102 of these cows were randomly assigned to 3 treatments: a 30-d DP with a standard energy level required for expected milk yield (30-d DP SEL; n = 36), a 0-d DP with the same energy level as cows with a 30-d DP (0-d DP SEL; n = 33), and a 0-d DP with a low energy level (0-d DP LEL, n = 33). From wk 8 of lactation onward, cows received either a glucogenic ration consisting of corn silage and grass silage or a lipogenic ration consisting of grass silage and sugar beet pulp at a standard or low energy level. During wk 1 to 7 postpartum, treatment did not affect SCC or SCC corrected for milk yield. During wk 8 to 44 of lactation, 0-d DP SEL cows had a greater SCC than 0-d DP LEL or 30-d DP SEL cows and had a greater SCC corrected for milk yield than 0-d DP LEL cows. During wk 1 to 44 of lactation, occurrence of at least 1 elevation of SCC (SCC ≥200,000 cells/mL after 2 wk of SCC <200,000 cells/mL) was not different among treatments. The 0-d DP SEL cows but not the 0-d DP LEL cows tended to have a 2.17 times greater hazard of having a case of clinical mastitis at any time in lactation than 30-d DP SEL cows. In wk 1 to 44 of lactation, lower fat- and protein- corrected milk yield and energy intake, greater energy balance, and greater plasma insulin concentration were associated with greater SCC. In conclusion, DP length did not affect udder health in the DP and in early lactation but seemed to decrease udder health for 0-d DP SEL cows in later lactation compared with 30-d DP SEL or 0-d DP LEL cows.

Consequences of dietary energy source and energy level on energy balance, lactogenic hormones, and lactation curve characteristics of cows after a short or omitted dry period.

Omitting the dry period (DP) generally reduces milk production in the subsequent lactation. The aim of this study was to evaluate the effect of dietary energy source-glucogenic (G) or lipogenic (L)-and energy level-standard (std) or low-on milk production; energy balance (EB); lactogenic hormones insulin, insulin-like growth factor 1 (IGF-1), and growth hormone (GH); and lactation curve characteristics between wk 1 and 44 postpartum in cows after a 0-d or 30-d DP. Cows (n = 110) were assigned randomly to 3 transition treatments: a 30-d DP with a standard energy level required for expected milk yield [30-d DP(std)], a 0-d DP with the same energy level as cows with a 30-d DP [0-d DP(std)], and a 0-d DP with a low energy level [0-d DP(low)]. In wk 1 to 7, cows were fed the same basal ration but the level of concentrate increased to 6.7 kg/d for cows fed the low energy level and to 8.5 kg/d for cows fed the standard energy level in wk 4. From wk 8 postpartum onward, cows received a G ration (mainly consisting of corn silage and grass silage) or an L ration (mainly consisting of grass silage and sugar beet pulp) with the same energy level contrast (low or std) as in early lactation. Cows fed the G ration had greater milk, lactose, and protein yields, lower milk fat percentage, greater dry matter and energy intakes, and greater plasma IGF-1 concentration compared with cows fed the L ration. Dietary energy source did not affect EB or lactation curve characteristics. In cows with a 0-d DP, the reduced energy level decreased energy intake, EB, and weekly body weight gain, but did not affect milk production or lactation curve characteristics. A 30-d DP resulted in a greater total predicted lactation yield, initial milk yield after calving, peak milk yield, energy intake, energy output in milk, days to conception [only when compared with 0-d DP(low)], plasma GH concentration [only when compared with 0-d DP(std)], and decreased weekly body weight gain compared with a 0-d DP. A 30-d DP decreased both the increasing and the declining slope parameters of the lactation curve and the relative rate of decline in milk yield (indicating greater lactation persistency) compared with a 0-d DP, and decreased plasma insulin and IGF-1 concentration, and EB. In conclusion, feeding a G ration after wk 7 in milk improved energy intake and milk production, but did not affect EB compared with an L ration. For cows without a DP, a reduced dietary energy level did not affect milk production and lactation curve characteristics, but did decrease EB and weekly body weight gain. A 30-d DP increased milk yield and lactation persistency, but decreased milk fat and protein content, EB, and plasma insulin and IGF-1, compared with a 0-d DP.

Relationships between uterine health and metabolism in dairy cows with different dry period lengths.

The first objective of this study was to evaluate effects of dry period (DP) length and dietary energy source on ovarian activity, uterine health status, pregnancy rate, and days open in dairy cows in the second subsequent lactation after implementation of DP length and dietary treatments. The second objective was to determine relationships of uterine health status with ovarian activity, milk yield, energy balance (EB), and metabolic status in dairy cows. Holstein-Friesian dairy cows (n = 167) were assigned randomly to 1 of 3 DP lengths (0-, 30-, or 60-d) and 1 of 2 early lactation diets (glucogenic or lipogenic diet) for 2 subsequent lactations. Milk samples were collected three times a week. At least two succeeding milk samples with concentration of progesterone ≥2 ng/mL were used to indicate the occurrence of luteal activity. Vaginal discharge was scored in wk 2 and 3 after calving to evaluate uterine health status and cows were classified as having a healthy uterine environment [HU, vaginal discharge score (VDS) = 0 or 1 in both wk 2 and 3], a recovering uterine environment (RU, VDS = 2 or 3 in wk 2 and VDS = 0 or 1 in wk 3), or a non-recovering uterine environment (NRU, VDS = 2 or 3 in wk 3). Cows were monitored for milk yield, dry matter intake (DMI), and blood was sampled weekly to determine metabolic status from calving to wk 3 postcalving. Dry period length was not related with uterine health status in early lactation, pregnancy rate, or days open in dairy cows. Independent of DP length, feeding a glucogenic diet shortened the interval from calving to onset of luteal activity (25.3 vs. 31.0 d, P = 0.04), but decreased pregnancy rate compared with a more lipogenic diet (68.2 vs. 78.1 d, P = 0.03). In the first 3 wk after calving, cows with a NRU had lower milk yield (36.8 vs. 36.8 vs. 32.4 kg for cows with a HU, RU, or NRU, respectively; P < 0.01) and lower DMI than cows with a HU or RU. Cows with a RU had lower plasma glucose and insulin concentrations than cows with a NRU or HU. In conclusion, DP length did not influence fertility measures and uterine health status in the second subsequent lactation after implementation of DP length treatments. Independent of DP length, feeding a glucogenic diet leaded to earlier ovulation postcalving, but decreased pregnancy rate compared with a more lipogenic diet. In addition, a healthy uterine environment was related to greater milk yield and better metabolic status, independent of DP length.

The effect of dry period length and postpartum level of concentrate on milk production, energy balance, and plasma metabolites of dairy cows across the dry period and in early lactation.

Shortening or omitting the dry period (DP) improves energy balance (EB) in early lactation because of a reduction in milk yield. Lower milk yield results in lower energy demands and requires less energy intake. The aim of this study was to evaluate the effects of DP length and concentrate level postpartum on milk yield, feed intake, EB, and plasma metabolites between wk -4 and 7 relative to calving of cows of second parity or higher. Holstein-Friesian dairy cows (n = 123) were assigned randomly to 1 of 2 DP lengths: 0-d DP (n = 81) or 30-d DP (n = 42). Prepartum, cows with a 0-d DP received a lactation ration based on grass silage and corn silage (6.4 MJ of net energy for lactation/kg of dry matter). Cows with a 30-d DP received a dry cow ration based on grass silage, corn silage, and straw (5.4 MJ of net energy for lactation/kg of dry matter). Postpartum, all cows received the same basal lactation ration as provided to lactating cows prepartum. Cows with a 0-d DP were fed a low level of concentrate up to 6.7 kg/d based on the requirement for their expected milk yield (0-d DP-L; n = 40) or the standard level of concentrate up to 8.5 kg/d (0-d DP-S; n = 41), which was equal to the concentrate level for cows with a 30-d DP (30-d DP-S; n = 42) based on requirements for their expected milk yield. Prepartum dry matter intake, concentrate intake, basal ration intake, energy intake, plasma ß-hydroxybutyrate (BHB), and insulin concentrations were greater and plasma free fatty acids (FFA) and glucose concentrations were lower, but EB was not different in cows with a 0-d DP compared with cows with a 30-d DP. During wk 1 to 3 postpartum, milk fat yield and plasma BHB concentration were lower and dry matter intake and concentrate intake were greater in cows with a 0-d DP compared with cows with a 30-d DP. During wk 4 to 7 postpartum, fat- and protein-corrected milk (FPCM), lactose content, and lactose and fat yield were lower in 0-d DP-L or 0-d DP-S cows compared with 30-d DP-S cows. Basal ration intake, EB, body weight, plasma glucose, and insulin and insulin-like growth factor-1 concentrations were greater and plasma FFA and BHB concentrations were lower in 0-d DP-L and 0-d DP-S cows compared with 30-d DP-S cows. Concentrate and energy intake were lower in 0-d DP-L cows than in 0-d DP-S or 30-d DP-S cows. Milk yield and concentrations of plasma metabolites did not differ in wk 4 to 7, although EB was lower in wk 6 and 7 postpartum in 0-d DP-L cows than in 0-d DP-S cows. In conclusion, a 0-d DP reduced milk yield and improved EB and metabolic status of cows in early lactation compared with a 30-d DP. Reducing the postpartum level of concentrate of cows with a 0-d DP did not affect fat- and protein-corrected milk yield or plasma FFA and BHB concentrations in early lactation but did reduce EB in wk 6 and 7 postpartum.

Effects of dry period length and dietary energy source on lactation curve characteristics over 2 subsequent lactations.

This study evaluated the effects of dry period (DP) length and dietary energy source on lactation curve characteristics over 2 subsequent lactations. It also evaluated the relationships of energy balance or metabolic status in early lactation with lactation curve characteristics in dairy cows. Holstein-Friesian dairy cows (n=167) were assigned randomly to 1 of 3 DP lengths (0-, 30-, or 60-d) and 1 of 2 early-lactation diets (glucogenic or lipogenic) for 2 subsequent lactations. In the second lactation following DP length treatments, 19 cows in the 0-d DP group were assigned to a 0→67-d DP group (actual days dry: 67±8d). Cows were allocated to this new group when they had a milk yield of <4kg/d at least 30d before their expected calving date. Fat- and protein-corrected milk (FPCM) was calculated weekly per cow in both lactations. Blood samples were taken weekly from calving to wk 4 after calving. A Wilmink lactation curve for each lactation was modeled based on FPCM yield records from calving through 305 DIM. During the first lactation following DP length treatments, cows with a 0- or 30-d DP had lower peak yield, later time of peak yield, and lower FPCM305 than cows with a 60-d DP. In the second lactation following DP length treatments, cows with a 0- or 30-d DP had lower peak yield than cows with a 60-d DP. In both lactations, lactation persistency was not affected by DP length and none of the lactation curve characteristics were affected by diet. In parity >2 cows, total FPCM yield and average daily FPCM yield throughout 2 lactations did not differ among DP lengths. In addition, average energy balance in the first 4wk after calving had a negative relationship with peak yield and FPCM305, and a positive relationship with lactation persistency. Average plasma concentrations of free fatty acids and ß-hydroxybutyrate had a positive relationship with peak yield and FPCM305, and a negative relationship with lactation persistency. Shortening or omitting the DP affected lactation curve characteristics in both lactations after implementation of DP length treatments but did not compromise FPCM yield compared with a conventional DP of 60d in parity >2 cows. Severe negative energy balance and poor metabolic status were related to greater peak yield, FPCM305, and lower lactation persistency.

The effects of dry period length and dietary energy source on natural antibody titers and mammary health in dairy cows.

In earlier studies, natural antibodies (NAb) were related not only to the energy balance (EB) of dairy cows, but also to somatic cell count (SCC) and clinical mastitis (CM). The first objective of our study was to evaluate the effects of dry period length and dietary energy source on titers of NAb binding keyhole limpet hemocyanin (KLH) and lipopolysaccharide (LPS) in plasma and milk, SCC and CM occurrence in dairy cows in two subsequent lactations. Our second objective was to study the relationship between NAb levels and mammary health. Holstein-Friesian dairy cows (N=167) were randomly assigned to three dry period lengths (0, 30 or 60-d) and two early lactation rations (glucogenic or lipogenic). Treatments were repeated during two subsequent lactations (years 1 and 2). In year 2, 19 cows which were planned to have 0-d dry period dried off naturally and were assigned to an additional group 0→30-d dry period. In year 1, cows with a 0-d dry period had a higher SCC, a higher titer of immunoglobulin G (IgG) binding LPS in plasma, and higher titers of IgG and IgM binding KLH and LPS in milk compared with cows with a 30-d or 60-d dry period. In year 2, cows with a 60-d dry period had a lower SCC than cows with a 30-d and 0→30-d dry periods. In year 2, dry period length did not affect NAb titers in plasma or milk. The CM occurrence was 17 percent in year 1 of the experiment and 25 percent in year 2, and did not differ according to dry period lengths or rations. For both years, an increasing titer of IgG binding LPS in plasma was associated with decreased odds of a high SCC and decreased odds of CM occurrence. Also up to three weeks before the CM occurrence, an increasing titer of IgM binding KLH and LPS in plasma was associated with a decreased odds of CM occurrence. In conclusion, omitting the dry period increased SCC, NAb titers in milk and IgG binding LPS in plasma compared with a short (30-d) or conventional (60-d) dry period. The effects on NAb titers, however, were only present in the first year after omitting the dry period and disappeared after repeated omitting the dry period. Moreover, an increasing titer of IgG binding LPS in plasma was associated with decreased odds of high SCC and CM occurrence.

Effects of dry period length and dietary energy source on milk yield, energy balance, and metabolic status of dairy cows over 2 consecutive years: Effects in the second year.

The objective of the current study was to evaluate the effect of dry period (DP) length on milk yield, energy balance (EB), and metabolic status in cows fed a lipogenic or glucogenic diet in the second year after implementation of DP and dietary treatments. Holstein-Friesian dairy cows (n=167) were assigned randomly to 1 of 3 DP lengths (0, 30, or 60d) and 1 of 2 early lactation diets (glucogenic or lipogenic) for 2 consecutive years. Results of the first year were reported previously. In the second year, 19 cows in the 0-d DP group were attributed to a new group (0→67d DP) because these cows had a milk yield of <4kg/d at least 30d before expected calving date and were dried off. Milk yield was recorded and EB was calculated from wk -8 to 9 relative to calving. Blood samples were taken weekly from wk -3 to 8 relative to calving. Liver samples were taken in wk -2, 2, and 4 relative to calving. At the onset of lactation, cows with a 0-d or 0→67-d DP had greater body condition score (BCS) than cows with a 60-d DP. During the first 9wk, cows with a 0- or 30-d DP produced 5.0 and 4.3kg less milk per day, respectively, but had similar EB compared with cows with a 60-d DP. Cows with a 0- or 30-d DP produced additional milk precalving, which could compensate milk yield losses in the first 9wk postcalving. Cows with a 0-d DP did not have milk yield losses or improve EB in the second year as much as in the first year. Cows with a 0-d DP had greater plasma insulin and insulin-like growth factor-I (IGF-I) and lower liver triacylglycerol concentrations than cows with other DP lengths. Cows with a 0→67-d DP had lower EB, and greater plasma free fatty acids (FFA) and ß-hydroxybutyrate (BHB) concentrations than cows with other DP lengths. Feeding a glucogenic diet increased plasma glucose, IGF-I, and insulin concentrations, and decreased plasma FFA, BHB, and urea concentrations compared with a lipogenic diet, independent of DP length. In conclusion, omitting the DP or feeding a glucogenic diet improved metabolic status in early lactation of the second year after implementation of DP length and dietary treatments, although effects of omitting the DP were less pronounced in the second year than in the first year. The less pronounced improvement of EB in the second year was related to the high BCS at the onset of lactation and reduced milk yield losses in cows with a 0-d DP.

Relationship between metabolism and ovarian activity in dairy cows with different dry period lengths.

The objectives of the present study were to evaluate the effects of dry period length on ovarian activity in cows fed a lipogenic or a glucogenic diet within 100 days in milk (DIM) and to determine relationships between ovarian activity and energy balance and metabolic status in early lactation. Holstein-Friesian dairy cows (n = 167) were randomly assigned to one of three dry period lengths (0, 30, or 60 days) and one of two diets in early lactation (glucogenic or lipogenic diet) resulting in a 3 × 2 factorial design. Cows were monitored for body condition score, milk yield, dry matter intake, and energy balance from calving to week 8 postpartum, and blood was sampled weekly from 95 cows from calving to week 8 postpartum. Milk samples were collected three times a week until 100 DIM postpartum for determination of progesterone concentration. At least two succeeding milk samples with progesterone concentration of 2 ng/mL or greater were used to indicate the occurrence of luteal activity. Normal resumption of ovarian cyclicity was defined as the onset of luteal activity (OLA) occurring at 45 DIM or less, followed by regular ovarian cycles of 18 to 24 days in length. Within 100 DIM postpartum, cows with a 0-day dry period had greater incidence of normal resumption of ovarian cyclicity (53.2%; 25 out of 47 cows) compared with cows with a 60-day dry period (26.0%; 13 out of 50 cows, P = 0.02). Independent of dry period length or diet, cows with OLA at less than 21 DIM had a greater body condition score during weeks 1 and 2 (P = 0.01) and weeks 1 through 8 (P = 0.01) postpartum compared with cows with OLA at greater than 30 DIM. Cows with the first ovarian cycle of medium length (18-24 days) had greater energy balance (P = 0.03), plasma concentrations of insulin (P = 0.03), glucose (P = 0.04), and insulin-like growth factor I (P = 0.04) than cows with long ovarian cycle lengths (>24 days) but had lower plasma ß-hydroxybutyrate (P < 0.01) and liver triacylglycerol (P = 0.02) concentrations than cows with short ovarian cycle lengths (<18 days) during weeks 1 through 8 postpartum. Diet did not affect the measured ovarian activity variables within 100 DIM. In conclusion, omitting the dry period (0 days) increased the incidence of normal resumption of ovarian cyclicity in dairy cows within 100 DIM compared with a conventional dry period (60 days). Short (<18 days) or long (>24 days) ovarian cycles during the first ovarian cycle postpartum were associated with severe negative energy balance and poor metabolic status in early lactation.

Effect of maternal dry period length on colostrum immunoglobulin content and on natural and specific antibody titers in calves.

The objective was to study the effect of dry period length in dairy cows on immunoglobulin content and natural antibodies (NAb) titers in colostrum, growth, and plasma natural and specific antibody titers in plasma of calves. Holstein-Friesian dairy cows (n=167) were randomly assigned to 3 dry period lengths (0, 30, or 60 d). Colostrum production, concentration of colostrum IgG and IgM, and titers of NAb (isotypes IgG and IgM) binding keyhole limpet hemocyanin (KLH) and human serum albumin (HuSA) in colostrum were measured. Female calves were immunized with both KLH and HuSA at wk 6 and 10 of life. Titers of NAb and specific antibody (SpAb) for isotypes IgG, IgM, and total immunoglobulin (IgT) binding KLH or HuSA were determined in plasma of female calves. Primary and secondary antibody responses to KLH or HuSA from wk 6 and 10 were expressed as the increase in antibody titers to wk 10 and 11 of life after primary and secondary challenges, respectively. Pregnancy length for cows with a 0-d dry period was 3d shorter compared with cows with a 30- or 60-d dry period. Birth weight of calves from cows with a 0-d dry period was lower compared with calves from cows with a 30-d dry period. Growth of calves until 12 wk of life was not affected by dry period length. Colostrum production and IgG and IgM concentration in colostrum were lower for cows with a 0-d dry period than a 60-d dry period. Natural IgG and IgM titers binding KLH or HuSA were lower in colostrum from cows with a 0-d dry period compared with cows with a 60-d dry period. Natural antibody titers (IgG, IgM, and IgT) binding KLH or HuSA in plasma were lower during the first 2 wk of life for calves from cows with a 0-d dry period compared with calves from cows with a 30- or 60-d dry period. After primary and secondary immunization of calves with KLH and HuSA, SpAb titers of calves were not affected by dry period length. After secondary immunization, the response of IgG and IgT binding KLH was higher in plasma of calves from cows with a 0-d dry period. The results of this study demonstrate that, although omission of the dry period of dairy cows leads to lower plasma NAb titers in calves during the first 2 wk of life, SpAb titers in calves were not affected and even the secondary antibody responses were enhanced compared with calves from cows with a 30- or 60-d dry period.

Effects of dry period length and dietary energy source on metabolic status and hepatic gene expression of dairy cows in early lactation.

In a prior study, we observed that cows with a 0-d dry period had greater energy balance and lower milk production compared with cows with a 30- or 60-d dry period in early lactation. The objective of the current study was to evaluate the influence of dry period length on metabolic status and hepatic gene expression in cows fed a lipogenic or glucogenic diet in early lactation. Holstein-Friesian dairy cows (n=167) were assigned randomly to 3×2 factorial design with 3 dry period lengths (n=56, 55, and 56 for 0-, 30-, and 60-d dry, respectively) and 2 early lactation diets (n=84 and 83 for glucogenic and lipogenic diet, respectively). Cows were fed a glucogenic or lipogenic diet from 10d before the expected calving date and onward. The main ingredient for a glucogenic concentrate was corn, and the main ingredients for a lipogenic concentrate were sugar beet pulp, palm kernel, and rumen-protected palm oil. Blood was sampled weekly from 95 cows from wk 3 precalving to wk 8 postcalving. Liver samples were collected from 76 cows in wk -2, 2, and 4 relative to calving. Liver samples were analyzed for triacylglycerol concentrations and mRNA expression of 12 candidate genes. Precalving, cows with a 0-d dry period had greater plasma ß-hydroxybutyrate, urea, and insulin concentrations compared with cows with a 30- or 60-d dry period. Postcalving, cows with a 0-d dry period had lower liver triacylglycerol and plasma nonesterified fatty acids concentrations (0.20, 0.32, and 0.36mmol/L for 0-, 30-, and 60-d dry period, respectively), greater plasma glucose, insulin-like growth factor-I, and insulin (24.38, 14.02, and 11.08µIU/mL for 0-, 30-, and 60-d dry period, respectively) concentrations, and lower hepatic mRNA expression of pyruvate carboxylase, compared with cows with a 30- or 60-d dry period. Plasma urea and ß-hydroxybutyrate concentrations were greater in cows fed a lipogenic diet compared with cows fed a glucogenic diet. In conclusion, cows with a 0-d dry period had an improved metabolic status in early lactation, indicated by lower plasma concentrations of nonesterified fatty acids, greater plasma concentrations of glucose, insulin-like growth factor-I, and insulin, and lower mRNA expression of pyruvate carboxylase in the liver, compared with cows with a 30- or 60-d dry period. Independent of dry period length, the glucogenic diet also improved the metabolic status compared with the lipogenic diet.

Cow characteristics and their association with production performance with different dry period lengths.

Shortening or omitting the dry period (DP) has been proposed as a management strategy to improve energy balance of dairy cows in early lactation. Both shortening and complete omission of the DP reduces milk production in the subsequent lactation compared with a conventional DP length of 60d. Some cows have less milk production loss than other cows after applying no DP or a short DP. The aim of this study is to evaluate which cow characteristics are associated with the amount of milk production losses following no DP or a short DP (30d). Daily production information from the lactation before and after the DP was available from 161 dairy cows (54 cows with a 0-d DP, 51 cows with a 30-d DP, and 56 cows with a 60-d DP) from a research herd. Daily production (milk, fat, and protein) until 305d in milk was estimated for all cows. Subsequently, total fat- and protein-corrected milk yield from 60d before the expected calving date until 305d in the following lactation (FPCMtotal) was estimated. A statistical analysis was performed to evaluate which cow characteristics were associated with limited or no production losses following no DP or a short DP, compared with a conventional DP length of 60d. Average FPCMtotal was 9,341, 10,499, and 10,795kg for cows with no DP, a 30-d DP, and a 60-d DP, respectively. The cow characteristics parity, daily milk production at 12wk before the expected calving date, and reduction in daily milk production between 16 and 12wk before the expected calving date were associated with production loss due to a short (30d) or no DP. Compared with 60d DP, multiparous cows had less production loss (987kg) following no DP than primiparous cows (2,132kg). The difference in FPCMtotal between the 3DP groups was largest for cows with a low milk production (e.g., 10kg/d) at 12wk before the expected calving date. The greater the reduction in milk production between 16 and 12wk before the expected calving date, the larger the difference in FPCMtotal between the 3DP groups. The difference in FPCMtotal between cows with no DP and 60d DP at a reduction in milk production between 16 and 12wk of 10% was 665kg, whereas this difference was 1,138kg at a reduction of 70%. The cow characteristics found can be used to select cows for specific DP lengths in a decision-support model to support the farmer on the economic optimal DP length for each individual cow. Output of such a decision-support model can be, for instance, to advise a 30-d DP for multiparous cows with high milk production (e.g., 25kg/d) at 12wk before the expected calving date.

Effect of dry period length and dietary energy source on energy balance, milk yield, and milk composition of dairy cows.

The objective of this study was to evaluate the effects of dry period length and dietary energy source in early lactation on milk production, feed intake, and energy balance (EB) of dairy cows. Holstein-Friesian dairy cows (60 primiparous and 108 multiparous) were randomly assigned to dry period lengths (0, 30, or 60 d) and early lactation ration (glucogenic or lipogenic), resulting in a 3 × 2 factorial design. Rations were isocaloric and equal in intestinal digestible protein. The experimental period lasted from 8 wk prepartum to 14 wk postpartum and cows were monitored for milk yield, milk composition, dry matter intake (DMI), energy balance, and milk fat composition. Prepartum average milk yield for 60 d precalving was 13.8 and 7.7 ± 0.5 kg/d for cows with a 0- and 30-d dry period, respectively. Prepartum DMI and energy intake were greater for cows without a dry period and 30-d dry period, compared with cows with a 60-d dry period. Prepartum EB was greater for cows with a 60-d dry period. Postpartum average milk yield until wk 14 was lower for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period (32.7, 38.7, and 43.3 ± 0.7 kg/d for 0-, 30-, and 60-d dry period, respectively). Postpartum DMI did not differ among treatments. Postpartum EB was greater for cows without a dry period and a 30-d dry period, compared with cows with a 60-d dry period. Young cows (parity 2) showed a stronger effect of omission of the dry period, compared with a 60-d dry period, on additional milk precalving (young cows: 15.1 kg/d; older cows: 12.0 kg/d), reduction in milk yield postcalving (young cows: 28.6 vs. 34.8 kg/d; older cows: 41.8 vs. 44.1 kg/d), and improvement of the EB postcalving (young cows: 120 vs. -93 kJ/kg(0.75)·d; older cows: -2 vs. -150 kJ/kg(0.75)·d. Ration did not affect milk yield and DMI, but a glucogenic ration tended to reduce milk fat content and increased EB, compared with a more lipogenic ration. Reduced dry period length (0 and 30 d) increased the proportion of short- and medium-chain fatty acids in milk fat and omitting the dry period decreased the proportion of long-chain fatty acids in milk fat. In conclusion, shortening and omitting the dry period shifts milk yield from the postpartum to the prepartum period; this results in an improvement of the EB in early lactation. An increased energy status after a short dry period can be further improved by feeding a more glucogenic ration in early lactation.

Carry-over of pyrrolizidine alkaloids from feed to milk in dairy cows.

Pyrrolizidine alkaloids are toxins present in many plants belonging to the families of Asteraceae, Boraginaceae and Fabaceae. Particularly notorious are pyrrolizidine alkaloids present in ragwort species (Senecio), which are held responsible for hepatic disease in horses and cows and may lead to the death of the affected animals. In addition, these compounds may be transferred to edible products of animal origin and as such be a threat for the health of consumers. To investigate the possible transfer of pyrrolizidine alkaloids from contaminated feed to milk, cows were put on a ration for 3 weeks with increasing amounts (50-200 g day(-1)) of dried ragwort. Milk was collected and sampled twice a day; faeces and urine twice a week. For milk, a dose-related appearance of pyrrolizidine alkaloids was found. Jacoline was the major component in milk despite being a minor component in the ragwort material. Practically no N-oxides were observed in milk, notwithstanding the fact that they constituted over 80% of the pyrrolizidine alkaloids in ragwort. The overall carry-over of the pyrrolizidine alkaloids was estimated to be only around 0.1%, but for jacoline 4%. Notwithstanding the low overall carry-over, this may be relevant for consumer health considering the genotoxic and carcinogenic properties demonstrated for some of these compounds. Analysis of the faeces and urine samples indicated that substantial metabolism of pyrrolizidine alkaloids is taking place. The toxicity and potential transfer of metabolites to milk is unknown and remains to be investigated.