Elena Bonfante

Effect of undigested neutral detergent fiber content of alfalfa hay on lactating dairy cows: Feeding behavior, fiber digestibility, and lactation performance

The objective of this study was to investigate the effects of 2 alfalfa hays differing in undigested neutral detergent fiber content and digestibility used as the main forage source in diets fed to high producing cows for Parmigiano-Reggiano cheese production. Diets were designed to have 2 different amounts of undigestible NDF [high (Hu) and low (Lu)], as determined by 240-h in vitro analysis (uNDF240). Alfalfa hay in vitro digestibility [% of amylase- and sodium sulfite-treated NDF with ash correction (aNDFom)] at 24 and 240 h was 40.2 and 31.2% and 53.6 and 45.7% for low- (LD) and high-digestibility (HD) hays, respectively. The 4 experimental diets (Hu-HD, Lu-HD, Hu-LD, and Lu-LD) contained 46.8, 36.8, 38.8, and 30.1% of alfalfa hay, respectively, 8.6% wheat straw, and 35.3% corn (50% flake and 50% meal; DM basis). Soy hulls and soybean meal were used to replace hay to balance protein and energy among diets. Eight multiparous Holstein cows (average milk production = 46.0 ± 5.2 kg/d, 101 ± 38 d in milk, and 662 ± 42 kg of average body weight) were assigned to a 4 × 4 Latin square design, with 2 wk of adaptation and a 1-wk collection period. Dry matter and water intake, rumination time, ruminal pH, and milk production and composition were measured. Diets and feces were analyzed for NDF on an organic matter basis (aNDFom), acid detergent fiber, acid detergent lignin, and uNDF240 to estimate total-tract fiber digestibility. Dry matter intake and rumination times were higher in HD diets compared with LD diets, regardless of forage amount. Rumination time was constant per unit of dry matter intake but differed when expressed as a function of uNDF240, aNDFom, or physically effective NDF intake. No differences were found among treatments on average ruminal pH, but the amount of time with pH <5.8 was lower in Hu-HD diets. Milk production and components were not different among diets. Total-tract aNDFom and potentially digestible neutral detergent fiber fraction digestibility was higher for the LD diets (88.3 versus 85.8% aNDFom in HD), for which lower feed intakes were also observed. The Hu-HD diet allowed greater dry matter intake, longer rumination time, and higher ruminal pH, suggesting that the limiting factor for dry matter intake is neutral detergent fiber digestibility and its relative rumen retention time.

A screening sampling plan to detect Mycobacterium avium subspecies paratuberculosis-positive dairy herds

Mycobacterium avium ssp. paratuberculosis (MAP) is the etiological agent of paratuberculosis, a chronic contagious bacterial disease primarily affecting dairy cattle. Paratuberculosis represents a dual problem for the milk production chain: in addition to economic losses to affected herds, MAP may have zoonotic potential. Infected herds must be identified in order to implement programs designed to reduce the incidence of disease within and between herds and to prevent MAP from entering the food chain. The objective of this study was to evaluate the sensitivity and specificity of a screening sampling plan (SSP) to detect MAP-positive dairy herds by repetitive analysis of bulk tank milk (BTM) samples by ELISA and in-line milk filter (ILMF) samples by PCR. Samples from BTM and ILMF were collected twice from 569 dairy herds in southern Italy. Additionally, 12,016 individual milk samples were collected: 9,509 from 102 SSP-positive herds (SSP MAP-positive) and 2,507 from 21 randomly selected SSP-negative herds (SSP MAP-negative). There was a total of 126 SSP MAP-positive herds (i.e., 21.3% SSP MAP-positive herds; 95% confidence interval=18.0-24.9); the within-herd apparent prevalence (AP) ranged between 0.00 and 22.73% (mean 6.07%). A significant difference in within-herd AP was shown between SSP MAP-positive herds and SSP MAP-negative herds. A highly significant association was shown between the median AP herd status (>5%) and positivity to at least one ILMF or BTM sample. The SSP detected a minimum of 56.25% of low AP herds (AP ≤ 2.0%) up to a maximum of 100% of herds with a within-herd AP ≥ 8.0%. Overall, the SSP detected 85.57% of herds in which at least one individual milk sample was positive by ELISA. The proposed SSP was an inexpensive and useful tool to detect MAP-positive herds with a higher risk of infection diffusion and milk contamination. Although the SSP cannot be used for MAP-free certification of herds, it could be useful to prioritize appropriate control measures aimed at reducing the prevalence of infection in dairy herds and milk contamination.

Effects of a completely pelleted diet on growth performance in Holstein heifers

Forage neutral detergent fiber (NDF) content and particle size are important factors that affect rumen function. The aim of the current study was to evaluate the effects on rumen health, NDF digestibility, and animal performance of pelleting a forage-based diet. Eight Holstein heifers (age 336±30d, body weight 346±35kg) were randomly assigned to a repeated crossover design. Animals were housed in tie-stalls and fed for ad libitum intake. The study included 4 periods of 3 wk, the first 2 wk for adaptation to the diet and the last wk for data collection. Diets had the same ingredients but had a different physical form: total mixed ration (TMR) and pellet (diameter=8mm). The physically effective NDF (peNDF) differed between the 2 treatments (39.8 and 11.8% of NDF in the TMR and pellet diets, respectively). During the trial, dry matter intake (DMI), water intake, rumination time, rumen temperature, and pH were evaluated daily. Fecal samples were collected in wk3 of each period to determine total-tract digestibility of the potential digestible (pd)NDF. Average daily gain and feed conversion ratio were calculated at the end of each period. With the pellet diet, DMI, DMI/body weight, and water consumption were higher. We observed no significant difference in average daily gain or feed conversion ratio. Rumination time was lower for the pellet diet than for the TMR diet (241 vs. 507min/d, respectively). Diet had no effect on rumen temperature or rumen pH. The total-tract digestibility of the pdNDF was greater with the TMR diet than with the pellet diet (90.25 vs. 86.82% pdNDF, respectively). The results of the current study suggest that a complete-feed pellet diet was well accepted by the animals, as demonstrated by higher DMI. Rumination time was reduced with the pellet diet, but rumen pH was not different. The pdNDF digestibility was high for both diets, but significantly higher for the TMR diet. Given that animal performance was similar between the 2 diets, although they differed with respect to DMI and fiber digestion, we hypothesize that the 2 diets had different retention times, related to their physical form. A complete-feed pellet diet formulated to provide a sufficient level of NDF from forages could be fed to growing ruminants without apparent negative effects on rumen health and animal productivity, at least for a short period. More research over a longer growing period is needed before recommending this feeding strategy for growing heifers.

Technical note: In vitro digestibility of amylase-treated, ash-corrected neutral detergent fiber, with addition of sodium sulfite, at 240 hours with or without rumen fluid reinoculation

Long-term in vitro fermentation (240 h) evaluating amylase-treated, ash-corrected neutral detergent fiber, with addition of sodium sulfite (aNDFom) digestibility is required to quantify the indigestible fiber fraction. It is commonly accepted to inoculate rumen fluid more than one time during such fermentations, every 96 h or at 120 h. However, no studies have been conducted to verify if the reinoculation is actually required to properly carry out the fermentation process. The current study aims to evaluate the effects of these procedures on aNDFom digestibility at 240 h. The study was conducted on a total of 24 forage samples (8 alfalfa hays, 8 grass hays, and 8 corn silages). Samples were digested in triplicate at 240 h in vitro. Rumen fluid was added twice (at 96 and 192 h) in treatment 1, after 120 h in treatment 2, whereas no addition was made in treatment 3. At the end of the fermentations, residual aNDFom was quantified to calculate digestibility. Among treatments, no difference was found in digestibility of aNDFom. Moreover, treatment 1 resulted in higher variability compared with other treatments. Results obtained in the current study show that subsequent addition of rumen fluid is not necessary for a proper estimation of aNDFom digestibility, and can be avoided.

Using single or multiple liquor-donor cows for in vitro digestibility of amylase- and sodium sulfite-treated neutral detergent fiber with ash correction

In vitro methods requiring ruminal microorganisms to ferment and digest feeds have been used for decades. Though commonly accepted, collecting and pooling rumen fluid from different donor animals to avoid individual characteristics could affect in vitro fermentations. The current study evaluated the effects of individual or pooled liquors on in vitro digestibility of amylase- and sodium sulfite-treated NDF with ash correction (aNDFom). The study was conducted on 24 samples (8 alfalfa hays, 8 grass hays, and 8 corn silages). The 3 donor animals (treatment 1, 2, and 3) were selected based on similar body weights, parity, days in milk, milk production, and milk composition. Samples were digested in vitro via inoculation of different rumen fluid at different time points (12, 24, 72, and 120h). An equal amount of each liquor collected was sampled and equally mixed with the others to obtain treatment 4. For the alfalfa hay group, differences were observed at 12 (29.95, 27.07, 29.02, and 32.55% aNDFom for treatments 1, 2, 3, and 4, respectively) and 24h (37.35, 35.54, 36.44, and 40.56% aNDFom for treatments 1, 2, 3, and 4, respectively). The inoculum source did not affect in vitro digestibility over longer time periods (72 and 120 h). Similar results were observed in the grass hay group, in which the mixed inoculum had greater digestibility values at both 12 (28.86, 26.89, 27.88, and 30.92% aNDFom for treatments 1, 2, 3, and 4, respectively) and 24h (37.35, 35.54, 36.44, and 40.56% aNDFom for treatment 1, 2, 3, and 4, respectively), but not over longer time periods. For the corn silage group, we observed differences for treatment 4 only at 12h (35.78, 33.87, 34.83, and 37.80% aNDFom for treatment 1, 2, 3, and 4, respectively). These results underline the differences among donor animals, especially when evaluating short incubation time points, and that pooling rumen contents is not equal to averaging across individual animals. Reported data require a deeper investigation on whether or not the method of inoculating a pool of rumen contents represents the actual ability of the animal to digest fiber.

Temporal variation of faecal shedding of Escherichia coli O157:H7 in a dairy herd producing raw milk for direct human consumption

The objective of this study was to analyse over time the evolution of E. coli O157:H7 faecal shedding in a dairy herd producing raw milk for direct human consumption. The study was performed between October 2012 and September 2013 in an average size Italian dairy farm where animals are housed inside the barn all over the year. The farm housed about 140 animals during the study – 70 cows and 70 calves and heifers. Twenty-six animals were randomly selected from both the cows and young animals group, and faecal sampling was performed rectally six times two months apart in each animal. Eleven animals were culled during the study and a total of 285 faecal samples were collected. At each faecal sampling, three trough water samples and two trough feed samples were also collected for a total of 36 water samples and 24 feed samples. Samples were analysed by real time polymerase chain reaction (RT-PCR) and culture. Overall, 16 (5.6%) faecal samples were positive for E. coli O157 by RT-PCR. Cultural examination found 9 (3.1%) samples positive for E. coli O157; all the isolates were positive for stx1, stx 2 and eae genes. One (4.1%) feed sample was positive for E. coli O157 by RT-PCR; none of the water samples was positive for E. coli O157. The model highlighted a general significant reduction of the number of positive samples observed during the study from the first to the sixth sampling (P=0.000) and a positive relation between the presence of positive samples and average environmental temperature (P=0.003). The results of the study showed that in an Italian dairy farm housing animals all year, faecal shedding of E. coli O157 followed the same temporal trend reported for other types of farming. The enhanced faecal shedding during warmer months may have a significant impact on environmental contamination and the safety of raw milk and its byproducts.

The term risk: etymology, legal definition and various traits

The etymology of the term risk and its legal qualification and definitions are reported in this article; decription of the various traits of the term risk used in food safety management (acceptable risk, current risk, emerging risk, crude risk, unrestricted risk, perceived risk, real risk, residual risk, reduced risk, baseline risk, serious risk, major technological risk, etc.) are presented and discussed.