J. Pantoja, J.L. Firkins, and M.L. Eastridge
Department of Animal Sciences
Holstein cows (50) were used to evaluate lactation performance and fatty acid digestibility (five cows) when fed fats varying in degree of saturation. Diets were a control with no added fat or four diets with 5% added fat from tallow, tallow plus partially hydrogenated tallow in proportions of 2:1 or 1:2, or partially hydrogenated tallow. Iodine values were 45, 35, 26, and 16, respectively. Fatty acid digestibility was lower for cows fed fat sources than for those fed the control diet and decreased linearly with increased fat saturation. In the digestion trial, cows fed fat tended to have lower dry matter intake (DMI) than those fed the control, primarily because of the unsaturated fat. In the production trial, DMI was similar for cows fed control (49.1 pounds/day) or tallow (48.6 pounds/day) and tended to be higher for cows fed partially hydrogenated tallow (52.6 pounds/day). In both trials, DMI increased linearly as fat saturation increased. Milk yield was higher for cows fed fat than for cows fed the control diet, but 4% FCM was not affected. Milk fat and protein percentages and body condition scores increased linearly with increased fat saturation.
Milk production in early lactation often is limited by energy intake. The addition of supplemental fat to dairy rations may improve the energy status of cows, but the net result depends on its effects on dry milk intake (DMI), fatty acid (FA) digestibility, and milk production. The negative effects of unsaturated fats on ruminal fiber digestion are documented. Partial hydrogenation of fat decreases inhibitory effects of unsaturated FA on ruminal fiber digestion, but the solubility and digestibility of FA in the small intestine are decreased. In contrast with results from unsaturated fat sources, DMI generally is not depressed when saturated fats are fed, although lower DMI has been reported in one study. In a summary of published data, we reported increased FCM yield and tendencies for increased percentages of milk fat and protein with increased iodine value (IV) of fat (more unsaturated). Our interpretation was somewhat limited because of the lack of data on milk production and composition to evaluate the effects of fat sources with IV between 20 and 50. Therefore, the present study was undertaken to evaluate the effect of feeding combinations of tallow and partially hydrogenated tallow (PHT) on FA digestibility, DMI, body condition score (BCS), and lactation performance by dairy cows.
Fifty Holstein cows (35 multiparous and 15 primiparous) were fed a pretreatment diet during weeks 2 and 3 of lactation for covariate adjustment of lactation performance data in the subsequent treatment period. Cows randomly were assigned to five diets within blocks to evaluate the effects of degree of fat saturation on DMI and lactation performance. Treatment diets were fed from weeks 4 to 19 of lactation. Diets were control with no supplemental fat, or diets with 5% fat from tallow, IV of 45; tallow and PHT in a proportion of 2:1 (diet T-PHT), IV of 35; tallow and PHT in a proportion of 1:2 (diet PHT-T), IV of 26; or PHT, IV of 16. Diets were formulated to meet or slightly exceed NRC guidelines for CP, NDF, minerals, and vitamins (Table 1). Cows were offered TMR that were mixed once daily but fed twice or more daily to keep feed in front of cows at all times. Samples of TMR from each diet were taken weekly, composited by month, and analyzed for nutrients using routine analyses.
| Table 1. Ingredient composition of experimental diets. | |||
| Diets | |||
| Ingredient | Pretreatment | Control | Fat |
| (% of DM) | |||
| Corn silage | 26.00 | 25.00 | 25.00 |
| Alfalfa silage | 26.00 | 25.00 | 25.00 |
| Soybean meal, 44% CP | 4.87 | 14.40 | 15.00 |
| Blood meal | 1.75 | 1.64 | 1.83 |
| Commercial supplement | 41.00 | . . . | . . . |
| Corn, ground shelled | . . . | 31.86 | 26.03 |
| Animal fat | . . . | . . . | 5.00 |
| Other | 0.38 | 2.10 | 2.14 |
Five cows were used in a 5 X 5 Latin square design to determine total tract digestion of nutrients of the same diets used in the production trial. Each experimental period consisted of 14 days; 9 days were for diet adaptation and 5 days were for data collection. Diets were mixed daily as TMR and fed twice daily. Chromic oxide was used as a digesta marker. Samples of TMR, feed refusals, and feces were analyzed for nutrients using routine analyses.
Cows in both trials were housed in a tie-stall barn and milked twice daily. Milk production was measured and recorded daily, and individual milk samples were taken at both milkings during 2 consecutive days per week for subsequent analysis of milk fat and protein concentrations by infrared spectroscopy (DHI Cooperative Inc., Powell, OH). Cows were weighed weekly. Body condition scores of the cows were determined at the beginning and end of the pretreatment period (start of weeks 2 and 4 of lactation) and every 28 days thereafter until the beginning of week 20 of lactation.
Data from the digestion trial were analyzed as a 5 X 5 Latin square design. Weekly data from the production trial were analyzed as a randomized complete block design. All data from the lactation trial, except BW change and energetic efficiency, were adjusted for the respective pretreatment data using covariate analysis. Treatment comparisons in both trials were effect of fat (control vs the average of tallow, T-PHT, PHT-T, and PHT), effect of tallow versus PHT, and linear and quadratic effects of degree of fat saturation for diets tallow, T-PHT, PHT-T, and PHT.
The composition of FA and the IV of fat sources are in Table 2. All diets met or slightly exceeded NRC guidelines for NDF and CP (Table 3). Diets supplemented with fat sources had higher NEL concentrations than did the control diet, and the adjusted NEL (ANEL) reflected the lower digestibility of the FA (Table 4) as the proportion of PHT in the diet increased.
Intake and apparent digestibilities of nutrients by cows used in the digestibility trial are in Table 4. The DMI tended to be lower for cows fed diets supplemented with fat than for those fed the control diet. Confirming our previous work, cows fed PHT had higher DMI than those fed tallow, and DMI increased linearly with increased degree of fat saturation. This negative response tended to increase as fat saturation decreased and fat supplementation increased. The effects of unsaturated fats on DMI may be due to gut fill, when ruminal fiber digestion is inhibited, or to postruminal effects (absorbed FA). In one study when FA were infused into the abomasum (bypassing the rumen), DMI decreased linearly as degree of fat saturation decreased
| Table 2. Fatty acid (FA) composition and iodine value of tallow and partially hydrogenated tallow (PHT). | ||
| FA1 | Tallow | PHT |
| (g/100 g of fatty acid) | ||
| 14:0 | 2.31 | 1.59 |
| 14:1 | 0.42 | . . . |
| 16:0 | 22.67 | 22.97 |
| trans-16:1 | 0.56 | 0.40 |
| cis-16:1 | 2.95 | 0.33 |
| 18:0 | 17.79 | 52.17 |
| trans-18:1 | 4.18 | 9.89 |
| cis-18:1 | 34.63 | 4.66 |
| 18:2 | 3.25 | . . . |
| 18:3 | 0.37 | 0.30 |
| 20:0 | 0.21 | 1.22 |
| Others | 10.66 | 6.49 |
| Iodine value2 | 45.0 | 16.4 |
| 1 Number of carbons: number of double bonds.
2 Calculated using FA concentrations. | ||
| Table 3. Chemical composition of experimental diets (DM basis). | ||||||
| Diets1 | ||||||
| Item | Pre | Control | Tallow | T-PHT | PHT-T | PHT |
| CP, % | 19.4 | 18.3 | 17.9 | 18.1 | 17.8 | 17.9 |
| NDF, % | 38.7 | 29.4 | 28.9 | 28.0 | 28.9 | 29.1 |
| ADF, % | 23.2 | 17.3 | 17.0 | 16.3 | 16.8 | 16.9 |
| Fatty acids, % | 2.57 | 2.90 | 6.13 | 6.80 | 6.58 | 6.54 |
| NEL, Mcal/kg | 1.60 | 1.71 | 1.82 | 1.86 | 1.83 | 1.83 |
| ANEL,2 Mcal/kg | 1.60 | 1.71 | 1.81 | 1.81 | 1.76 | 1.74 |
| Ca, % | 0.96 | 0.98 | 0.96 | 0.98 | 0.82 | 0.89 |
| P, % | 0.50 | 0.45 | 0.45 | 0.48 | 0.43 | 0.43 |
| Mg, % | 0.29 | 0.32 | 0.29 | 0.36 | 0.33 | 0.28 |
| K, % | 1.46 | 1.18 | 1.14 | 1.06 | 1.03 | 1.07 |
| 1 Diets were pretreatment (Pre), control, 5% fat from tallow (T) with an iodine value (IV) of 45, 5% fat from tallow
and partially hydrogenated tallow (PHT) in a proportion of 2:1 with an IV of 35 (T-PHT), 5% fat from tallow and
PHT in a proportion of 1:2 with an IV of 26 (PHT-T), and 5% fat from PHT with an IV of 16 (PHT).
2 Adjusted NEL calculated by standardizing fatty acid digestibility of fat-supplemented diets relative to that of the control diet. | ||||||
Apparent total tract digestibilities of DM, NDF, and N were not affected by fat supplementation, fat source, or degree of fat saturation (Table 4). In our previous study, decreasing the degree of fat saturation linearly decreased digestibility of NDF in the rumen but not in the total tract. Shifts in the site of NDF digestion probably occurred but were not detected in other studies in which unsaturated fats were fed and only total tract digestion was measured. Total FA digestibility was lower for cows fed diets supplemented with fats than for those fed the control diet, mainly because of the lower digestibility of PHT in the small intestine. Researchers from Clemson University reported a positive associative effect of combining saturated and unsaturated fat, but within the range of IV used in the current study, no such association (i.e., no quadratic response) was detected.
In contrast with data from the digestion trial, DMI was not affected by fat supplementation (control vs average of fat diets) in the lactation trial (Table 5). The contrast among trials may be related to the amount of time given for adjustment to diets supplemented with fat or to stage of lactation. Reported depressions of DMI caused by fat generally were with early lactation cows. However, researchers from the University of New Hampshire reported no advantage in DMI by delaying the introduction of Ca soaps of FA into the diets of early lactation cows. The trend for higher DMI by cows fed PHT than for those fed tallow and the linear increase in DMI with increased fat saturation is in agreement with data of the digestion trial (Table 4) and with previous literature reports. When NEL was adjusted for the digestibility of FA (ANEL), the linear effect of DMI was negated, and a tendency for a quadratic effect on ANEL intake was observed (Table 5). Cows fed T-PHT tended to have lower DMI than those fed the other treatments, although no biological reason is apparent.
Milk production was higher for cows fed diets containing fat than for those fed the control diet. Milk production typically increases with fat supplementation because of greater NEL intakes or higher efficiency of milk synthesis, but no significant effects have been reported in some studies. Neither adjusted NEL intake nor energetic efficiency were significantly affected by treatment in our study, perhaps because of variation or a combination of both effects increasing milk production by cows fed fat. As in a previous Ohio State University study, cows fed tallow had a lower milk fat percentage than did those fed PHT. Milk fat percentage increased linearly as fat saturation increased. Milk fat yield was not affected by any of the dietary treatments.
In contrast to results of previous reports, milk protein percentage was similar in cows fed the control diet or diets supplemented with fat. However, cows fed PHT had a higher milk protein percentage than did those fed tallow. Milk protein percentage increased linearly as degree of fat saturation increased. In a literature analysis, we observed that increased fat saturation, on average, increased milk protein percentage. The effects of fat supplementation on milk protein percentage are not totally understood. The depression in milk protein percentage that often is observed when cows are fed supplemental fat has been attributed to increased efficiency of energy utilization and decreased blood flow to the mammary gland. Other researchers theorized that milk protein depression for cows fed fat is due to decreased DMI and insufficient amounts of critical amino acids for milk protein synthesis as milk synthesis increases. The increased DMI with decreased IV of fat may result in a higher supply of amino acids for milk protein synthesis, supporting the latter theory. Production of 4% FCM was similar among diets, but, when expressed as a proportion of DMI, tended to be higher in cows fed fat than in those fed the control diet.
Cows fed the control diet lost more BW than did cows fed diets supplemented with fat, despite similar DMI and lower milk production. In a continuous lactation trial done at the University of Wisconsin, cows fed fat at 3% of the dietary DM in early lactation gained more BW than did those fed diets with no supplemental fat. Production of 4% FCM per ANEL intake and energetic efficiency were not affected by fat supplementation, although average BCS was numerically lowest for cows fed the control diet.
No effects from fat source or degree of fat saturation on BW change were detected. Cows fed PHT had a significantly higher average BCS than those fed tallow, and BCS increased linearly as degree of fat saturation increased. These data provide support that increasing saturation of fat in the diet increased body fat deposition, but data for BW change probably were too variable for detection of significant treatment differences, or perhaps body composition changes were not reflected in BW change. These data support the value of BCS, apart from BW and size, as a measure of the cows' energy reserves.
The decreased FA digestibility with increased degree of fat saturation (decreased IV) was offset by linear increases in DMI and BCS and in percentages of milk fat and protein.These results, combined with a milk price structure with emphasis on nonfat milk solids, may indicate potential economical advantages with the use of PHT.
| Table 4. Intake and apparent digestibility of nutrients in the total tract of cows fed no supplemental fat or tallow differing in degree of saturation during the digestibility trial. | ||||||||||
| Probabilities of contrasts2 | ||||||||||
| Diets1 | C vs fat | Tallow vs PHT | Saturation | |||||||
| Item3 | Control | Tallow | T-PHT | PHT-T | PHT | SE | L | Q | ||
| DMI, kg/day | 25.2 | 23.1 | 23.8 | 24.8 | 24.7 | 0.5 | 0.07 | 0.04 | 0.02 | 0.50 |
| DMI, % of BW | 4.28 | 3.91 | 4.01 | 4.21 | 4.21 | 0.08 | 0.05 | 0.02 | 0.01 | 0.50 |
| Total FA intake, g/day | 721 | 1513 | 1623 | 1713 | 1643 | 53 | 0.01 | 0.11 | 0.07 | 0.12 |
| Apparent digestibility, % Dry matter | 69.3 | 68.2 | 65.5 | 67.1 | 67.8 | 1.4 | 0.19 | 0.81 | 0.98 | 0.24 |
| NDF | 48.4 | 48.0 | 46.0 | 48.6 | 50.5 | 3.9 | 0.97 | 0.66 | 0.57 | 0.63 |
| Nitrogen | 70.4 | 69.6 | 68.5 | 68.8 | 69.4 | 1.0 | 0.24 | 0.91 | 0.97 | 0.39 |
| Total FA | 75.1 | 73.1 | 64.6 | 59.8 | 59.8 | 57.1 | 1.9 | 0.01 | 0.01 | 0.16 |
| Total C16 FA | 73.3 | 78.3 | 68.5 | 62.6 | 56.6 | 2.4 | 0.02 | 0.01 | 0.01 | 0.45 |
| Total C18 FA | 75.9 | 70.3 | 62.0 | 57.8 | 55.8 | 2.1 | 0.01 | 0.01 | 0.01 | 0.17 |
| 1 Diets were control, 5% fat from tallow (T) with an iodine value (IV) of 45, 5% fat from tallow and partially hydrogenated tallow (PHT) in a
proportion of 2:1 with an IV of 35 (T-PHT), 5% fat from tallow and PHT in a proportion of 1:2 with an IV of 26 (PHT-T), and 5% fat from PHT with IV of 16
(PHT). Data are means from five cows per treatment.
2 Probabilities of contrasts: effect of fat (C vs T, T-PHT, PHT-T, and PHT); effect of fat source (T vs PHT); linear (L) and quadratic (Q) effects of fat saturation in T, T-PHT, PHT-T, and PHT diets. 3 DMI = dry matter intake, BW = body weight, and FA = fatty acid. | ||||||||||
| Table 5. Least squares means for lactation performance by cows fed no supplemental fat or tallow differing in degree of saturation during wk 4 to 19 of lactation. | ||||||||||
| Probabilities of contrasts2 | ||||||||||
| Diets1 | C vs fat |
Tallow
vs PHT |
Saturation | |||||||
| Item3 | Control | Tallow | T-PHT | PHT-T | PHT | SE | L | Q | ||
| DMI, kg/day | 22.3 | 22.1 | 21.2 | 22.5 | 23.9 | 0.7 | 0.90 | 0.08 | 0.04 | 0.13 |
| BW, kg | 553 | 551 | 552 | 546 | 563 | 8 | 0.97 | 0.30 | 0.40 | 0.34 |
| DMI, % of BW | 3.97 | 3.95 | 3.78 | 4.14 | 4.29 | 0.12 | 0.60 | 0.05 | 0.01 | 0.18 |
| NEL intake, Mcal/day | 38.5 | 40.3 | 38.8 | 40.5 | 43.3 | 1.4 | 0.15 | 0.13 | 0.09 | 0.13 |
| ANEL intake, Mcal/day | 38.5 | 40.1 | 37.8 | 39.0 | 41.2 | 1.3 | 0.50 | 0.57 | 0.46 | 0.10 |
| Milk, kg/day | 35.6 | 40.6 | 36.9 | 39.3 | 38.0 | 1.3 | 0.04 | 0.18 | 0.37 | 0.36 |
| Milk fat, % | 3.63 | 3.17 | 3.48 | 3.56 | 3.77 | 0.14 | 0.40 | 0.01 | 0.01 | 0.72 |
| Milk fat, g/day | 1282 | 1303 | 1293 | 1361 | 1403 | 57 | 0.37 | 0.24 | 0.18 | 0.65 |
| Milk protein, % | 3.05 | 2.86 | 3.03 | 2.98 | 3.02 | 0.05 | 0.17 | 0.03 | 0.07 | 0.21 |
| Milk protein, g/day | 1086 | 1156 | 1113 | 1163 | 1144 | 36 | 0.17 | 0.82 | 0.93 | 0.75 |
| 4% FCM, kg/day | 33.6 | 35.6 | 33.6 | 36.3 | 36.3 | 1.2 | 0.16 | 0.69 | 0.39 | 0.39 |
| 4% FCM/DMI | 1.52 | 1.61 | 1.61 | 1.64 | 1.57 | 0.04 | 0.07 | 0.48 | 0.60 | 0.37 |
| 4% FCM/ANEL intake | 0.89 | 0.89 | 0.90 | 0.94 | 0.91 | 0.02 | 0.45 | 0.66 | 0.43 | 0.44 |
| BW change4, kg/week | -2.16 | -0.53 | 1.09 | 0.13 | 0.04 | 0.95 | 0.03 | 0.67 | 0.86 | 0.37 |
| Energetic efficiency4,5 | 1.14 | 1.21 | 1.21 | 1.23 | 1.15 | 0.04 | 0.31 | 0.32 | 0.38 | 0.34 |
| BCS | 2.13 | 2.17 | 2.35 | 2.33 | 2.56 | 0.13 | 0.14 | 0.04 | 0.06 | 0.86 |
| 1 Diets were control, 5% fat from tallow (T) with an iodine value (IV) of 45, 5% fat from tallow and partially hydrogenated tallow (PHT) in a
proportion of
2:1 with an IV of 35 (T-PHT), 5% fat from tallow and PHT in a proportion of 1:2 with an IV of 26 (PHT-T), and 5% fat from PHT (PHT) with IV
of 16. Data are for means of ten cows per treatment.
2 Probabilities of contrasts: Effect of fat (control vs T, T-PHT, PHT-T, and PHT); effect of fat source (T vs PHT); linear (L), and quadratic (Q) effects of fat saturation in T, T-PHT, PHT-T, and PHT diets. 3 DMI = dry matter intake, BW = body weight, ANEL = NEL adjusted for differences in fatty acid digestibility, FCM = fat-corrected milk, and BCS = body condition score, which was measured using a scale of 1 to 5 at the beginning of weeks 4, 8, 12, 16, and 20 of lactation. 4 Data were not covariate-adjusted. 5 Energetic efficiency = (ECM + NEM + NEL for BW change)/ANEL intake; ECM = energy-corrected milk. | ||||||||||