Cost-Benefit Analysis of Pastured Pig Weight Gains With and Without Added Protein Supplements

1. Methods

         a. Specifics:   

3 groups of mixed heritage/commercial breed hogs consisting of 9 hogs in each group were fed three different ad-libitum feed mixes (one group per mix). The mixes were as follows:

1. Wheat and mineral mix: WM
2. Wheat, mineral mix, and lysine: WML
3. Wheat, mineral mix, lysine, and GMO-free canola meal: WMLC

  Each individual pig will correspond with their respective group acronym (WM, WML, WMLC) in all results, as well as their individual tag number.

  Pigs were weighed with a Waypig 500, which has an expected accuracy of within three lbs. All pigs were determined to be healthy at the beginning of the study.

All pigs were wormed using fenbendazole for (5) days two weeks prior to the study start time to insure parasites would not be a factor. Each group of pigs were given 2 acres of perennial pasture consisting of native and non-native common pasture plants, containing about 85% preferred hog forage. The three groups’ were randomized so that the starting weights of each group averaged around 156 lbs (with ~2 lb. differential). Each group had 6-7 “heritage cross” pigs and 2-3 “commercial cross” pigs. All study pigs were of 5-6 months of age. They were sorted, tagged and given roughly two acres of vegetation each (separated by two polywire strands) from August 28th to September 25th, 28 days total.

Feed consumption was calculated assuming the number of 50 lb. bags used during the experiment. We assumed 20% feed loss in each group due to the nature of our feed choice system (open bins), which was affected by rain, trampling and mud and had to occasionally be dumped and replaced. All groups had equal access to clean feed. Water was free choice, and each group had one 75-gallon tub, which was replaced daily. All pigs had equal access to hedgerow and wallows for weather protection and temperature regulation.

2. Hog Selection

        a. Hog Genetics

Two sources of hog genetics were used in the experiment.  The first was pigs farrowed on-farm. This line of pigs was started by crossing a purebred lard-type Mulefoot boar to purebred commercial Duroc sows.  50/50 Mulefoot/Duroc sows were crossed back to a purebred Gloucestershire Old Spot boar. Future generations were crossed to boars containing Hereford, Yorkshire and Berkshire genetics.  At that point the herd was closed and all selection happened from within the herd. Primary selection criteria for both boars and sows were 1) maternal instincts for open pen farrowing, 2) confirmation and growth characteristics and 3) temperament.  All hogs selected from this source are labelled “heritage cross” in table 5.

The second source of hogs was bought in from another breeder.  These pigs were yorkshire & duroc crosses- a more commercial hog.  They are labelled “commercial cross” in table 5.

Table 1: Feed Recipes & Costs

3. Pasture/Forage Analysis

         a. The Pasture Sward

Paddocks were chosen that gave the pigs unlimited forage access in a best case scenario for a perennial pig pasture. We originally planned to graze the research pigs on a mix of brassicas and Durana white clover, but experienced a drought during the first half of the season which stunted their growth, and found the brassicas to be less competitive than pre-established species. We then switched our focus to naturally occurring perennial pasture, which is what we and most other known operations use to graze anyway. The field chosen had been rotationally grazed with pigs 2-3 times per season for 8 years.  The grazing has always been done with high stock density (300 hogs averaging 150 lbs per ¼ acre - 180,000 lbs of pig per acre) and short duration (1-4 days per paddock). The field was not mowed in this time.

The study began in the paddocks on August 28th after a dry spring/early summer and a wet late summer.  The field was grazed in May and June and was allowed to regrow until the start date, a regrowth period of about 75 days.  The vegetation was lush but “overmature” for making high quality hay. The goal was to give them essentially unlimited forage.  At the end of the experiment plentiful high quality forage remained in the paddocks.

Pasture composition was typical of rotationally grazed hog pasture - high plant diversity, consisting of a variety of annuals and perennials and including nutrient-loving annuals (lambsquarters).  The most commonly found plant species included perennial grasses, white clover, red clover, dandelion, curly dock, burdock, morning glory, lambsquarters, redroot pigweed, chickweed, canada thistle, milkweed, goldenrod and asthers. While there was some variation, paddocks were largely similar in their forage variety make-up.

A diverse pasture sward is ideal to suit the grazing nature of hogs. Through our observation during this study and over the years of pasturing pigs, we’ve seen pigs are high selective in their grazing habits (unlike cattle, for instance).  As they walk through the paddock, they may take a single bite of curly dock, then eat a young thistle, and then a dandelion leaf. They prefer the lower fiber broadleaf “weeds” to grasses generally, although they have a technique for maximizing the value of grasses.  The hogs will take a mouthful of grasses, masticate them, drink the juices and spit out the fibers into a “puck”. This allows them to get the highly digestible water soluble sugars and proteins without filling up on relatively indigestible fiber. The highly selective nature of hogs allows them to always find forage at an acceptable stage of maturity and avoid overmature or fibrous forages.

             Photo: a ball of grass fibers after a pig has chewed it at length.

Generally speaking, they graze rather than root, although localized rooting was observed, mostly around colonies of Canada Thistle, which spread through rhizomes.  Interestingly, the rooted up areas provide surface soil access for the seeds of the very annuals and biennials that the pigs prefer - dandelion, lambsquarters, etc.  The rooting also encourages regrowth of canada thistle shoots - a preferred, high protein forage.

      b. Forage Testing and Analysis

Observation of the pigs showed that their preferred forages were white clover, curly dock, dandelion, chickweed, lambsquarters, canada thistle and young grasses.  Samples of each of these plants were collected from the actual paddocks the pigs were grazing during the experiment and sent for forage testing. The forage testing clearly showed that the available forages provided high quality, high protein fodder.

It should be mentioned that in addition to the plant varieties below, a negligible amount of fallen tree nuts and fruits (acorns, black walnuts and wild apples) were also accessible within each group’s paddocks. Our analysis also does not include nutrients obtained via rooting such as tubers or grubs, which we speculate provided some additional protein and minerals.

Table 2: ESTIMATED % OF PASTURE COVERAGE, BY VARIETY OF FORAGE

Table 3: NUTRITION COMPOSITION OF PREFERRED FORAGE

*conducted at Dairy One Labs, 730 Warren Road, Ithaca, New York 14850